Erosional surfaces and glacial geology along the southwest flank of the Crazy Mountains, Montana
by John P Bluemle
A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
Master of Science in Applied Science with a major in Geology
Montana State University
© Copyright by John P Bluemle (1962)
Abstract:
Significant and interesting geomorphic-glacial relations along the southwest margin of the Crazy
Mountains provide data for an understanding of a series of late Cenozoic surfaces. Paleocene (Fort
Union) sandstones, into which stocks, sills and dikes have been intruded, comprise the relatively
homogeneous sedimentary succession underlying the area. The gently northerly dipping beds do not
greatly affect the geomorphology of the area.
Four surface systems, formed by laterally planating streams issuing from the Crazy Mountains, are of
the following ages.
Surface I ----- early Pleistocene or late Pliocene Surface II ---- early to mid-Pleistocene Surface III---early Wisconsin Surface IV ---- intra-Wisconsin Gravels, probably indicative of older surface
remnants, are also present on high benches above surface I. Although the present Yellowstone River
flows eastward, the presence in the Gallatin Valley of gravels from the Crazy Mountains, suggests that
drainage prior to the cutting of surface I was directed westward.
In the north, erosion since the latest glacial advance has been confined to deep, narrow valleys, whereas
in the south, where erosion has been more effective, valleys are wide and only small remnants of the
earlier surfaces remain.
Ages of the two youngest surfaces were determined after appraisal of their relationships with glacial
features. Two substages of Wisconsin glaciation are recognized; the latest moraine is fresh, the earliest
quite subdued. They are easily distinguished in the field by comparison.
Contrary to Alden's (1932) belief, I have classified surface II as Pleistocene and therefore younger than
the Flaxville Plain as it was defined in northern Montana.
Statistical studies indicate increasing sphericity and roundness and decreasing size with transport
distance except on the oldest surface. The studies show that the three younger surfaces were
stream-carved, but the oldest surface has undergone modifying influences, due either to its greater age
and length of exposure or reworking by glaciers. EROSIONAL SURFACES AND GLACIAL GEOLOGY
ALONG THE SOUTHWEST FLANK OF THE
CRAZY MOUNTAINS, MONTANA
by
JOHN P. BLUEMLE
iA
t h e s i s subm itted to th e Graduate F acu lty in p a r t i a l
f u l f i l l m e n t o f th e requirem ents f o r th e degree
of
iMAsTer o f S c i e n c e i n A p p l i e d S c i e n c e
w i t h a m a j o r i n Geol ogy
'Approved:
Head, Major D e p a r tm e n t
-------^haifm an,
E x a m in in g Committed
MONTANA STATE COLLEGE
Bozeman, Montana
A pril,
1962
TABLE OF CONTENTS
page
INTRODUCTION............................................................................................................................................. .1
L o c a t i o n , .................................. .... . •..................................................... ....
I
P u r p o s e s o f T h i s S t u d y .......................................................... .... ............................ .... . .
I
G e n e r a l P h y s i o g r a p h y . ........................................................................
.2
P r e v i o u s I n v e s t i g a t i o n s ................... . ....................................... . . . . . . .
3
A c k n o w le d g e m e n t s . . . . . . . .
i .................................... . . . .
4
REGIONAL GEOLOGY............................
I n t r o d u c t i o n . ............................................ »
,
S t r a t i g r a p h y . ...................................................................................................................
St r u c t u i e . » » * . . . . . . . , . » .. . » . . »
, . .. . . . « *
5
5
5
0
LIST OF MAJOR CONCLUSIONS..............................................................
9
PROMINENT IRREGULAR
TOPOGRAPHIC
FEATURES.
;
IO
SURFACES SOUTHWEST OF THE MOUNTAINS........................................................................ . 16
I n t r o d u c t i o n . ......................................
16
S u r f a c e I ......................................................
17
S u r f a c e I I . ...........................................
. 24
S u r f a c e I I I ........................................................... ... ............................................... . . . .
32
S u r f a c e IV...................................................................
.37
S h i e l d s R i v e r T e r r a c e s ...................................................................
41
Alluvium. . . . »
........................................................................ . . . . . . . . .
42
RESULTS OF THE STATISTICAL STUDIES. . . . . . . . . . .
........................... . 43
Method o f D e t e r m i n i n g S p h e r i c i t y ............................
44
Method o f D e t e r m i n i n g R ou nd ne ss . . .
.......................
44
S i z e o f P a r t i c l e s ............................................................................
.4 5
C o m p o s i t i o n . ...........................................
45
D iscussion o f th e Graphs. . . . .
............................. . . . . . . . . . .
45
STREAM AND DRAINAGE CHARACTERISTICS . . ........................................................................52
I n t r o d u c t i o n .................................
52
Cot to nw oo d C r e e k ......................................
52
Rock C r e e k ....................................................................................................................................... 5 3
O t h e r S t re a m s . ......................................................................................................................... 5 5
GLACIATION AND ITS CONSEQUENCES...............................................
57
I n t r o d u c t i o n ..........................................................................................
57
Rock C r e e k V a l l e y G l a c i e r s . . . . . . .
j
. . . . . . . . . . . . .
i 50
Duck C r e e k V a l l e y G l a c i e r ................... . ............................. . . . . . . . .
60
Cot to nw oo d C r e e k V a l l e y G l a c i e r s .................................
62
O t h e r G l a c i a l F e a t u r e s and Summary.................................
67
CONCLUSIONS AND SUMMARY . . '..................................................... .... ....................... ....
Number and C a u s e s o f E r o s i o n a l S t a g e s ......................................
Methods o f S u r f a c e C o n s t r u c t i o n ...........................................
D iscussion of the F la x v il i e P lain . . . . .
.................................. » . . .
Ages o f t h e S u r f a c e s .........................................................
G e n e r a l C o m p a r i s o n s and C o r r e l a t i o n s ................................................
68
68
71
75
80
87
APPENDIX A - TECHNICAL DATA............................. ........................................................................91
Base Map . . .................................. .... ................................................................................. .... . 92
P rofiles
........................ ............................ ....
92
P h o t o g r a p h y . .................................................................... ....
93
STATISTICAL STUDIES,
. . . . .
....................................................................................... 93
APPENDIX B - SUMMARY OF THEORIES ADVANCED TO EXPLAIN THE FORMATION OF
PEDIMENTS.................................................................................. ....
138
Introduction
....................................... . . . . . . . .
.1 3 9
M ajo r I d e a s About t h e O r i g i n o f P e d i m e n t s . . . . . . . . . . . . .
.1 4 0
SELECTED REFERENCES
.1 4 5
L IS T OF TABLES
page
Table I
Table 2
R e g i o n a l c o r r e l a t i o n c h a r t ......................................................................... 86
S u r f a c e c o r r e l a t i o n t a b l e ......................................................................... 88
L IS T OF FIGURES
page
Figure
Figure
Figure
Figure
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Figure
I
2
3
5
6
7
8
9
10
11
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12
13
14
15
16
17
18
19
20
21
4
F i g u r e 22
Figure
Figure
Figure
Figure
Figure
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Figure
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Figure
23
24
25
26
27
28
29
30
31
32
F i g u r e 33
F i g u r e 34
Figure
Figure
Figure
Figure
Figure
Figure
Figure
35
36
37
38
39
40
41
F i g u r e 42
Geomorphic Map o f t h e S o u t h w e s t C r a z y Mou nta in Area , „in p o c k e t
I n d e x Map o f M o n ta n a ............................... * .......................................................... 3
M ajo r T e c t o n i c F e a t u r e s Near t h e C r a z y M o u n ta i n s . . . . . .
7
I b e x Mou nta in . . . . . . . . . . . . . . . . . . . . .
6 , 11
Dike Sout h o f Duck C r e e k M o r a i n e ................................... ..... . . . .
12
F a l l s Creek Canyon. . . . . . . . . . . . . . . . . . . .
13
Dike N or th o f F a l l s C r e e k ............................................
14
Sq u a w 's T i t .................................................
. 16
View o f S u r f a c e I . ............................................................................................19
G r a v e l C ov e r on S u r f a c e I . . . . .
............................................ . 20
S c h e m a t i c i l l u s t r a t i o n showing how t h e amount o f
c r y s t a l l i n e m a t e r i a l b e i n g removed from t h e m o u n t a i n s
in c re a se s with tim e. . . . . . . . . . . . .
........................ 21
View tiver Rock C r e e k a t S u r f a c e I I and S u r f a c e I . . . . . . 25
View n e a r t h e hea d o f S u r f a c e I I . . . . . . . . . . . . .
25
Remnants o f S u r f a c e I I . . . . . . . . . . . . . . . . . .
26
S u r f a c e I I a b o u t two m i l e s n o r t h e a s t o f C h a d b o r n . . . . .
26
Panorama o f s e v e r a l s u r f a c e s . . . .
......................... . . . . .
27
T y p i c a l g r a v e l c a p on S u r f a c e I I .........................
28
S h i e l d s R i v e r n e a r C h a d b o r n ..................................................................... 3 3 ,
S h ie ld s R iver v a lle y n o rth o f Chadborn. . . j . . . . . .
33
S h i e l d s R i v e r v a l l e y s o u t h o f C h a d b o r n ................................................ 34
C o m p o s it e p r o f i l e s o f s u r f a c e s s o u t h w e s t o f t h e C r a z y
M o u n ta i n s a s s e m b l e d a c c o r d i n g t o e s t i m a t e d r e l a t i v e
p o s i t i o n s . ............................................................... .... ............................ . . 40
I n d e x map sh owing l o c a t i o n o f s a m p l e s u s e d i n t h e .
s t a t i s t i c a l s t u d i e s . ............................................................................ . 46
Graph sh owing s p h e r i c i t y v s . d i s t a n c e .......................... . . . .
48
Graph showing c o m p o s i t i o n v s . d i s t a n c e . . . . . . . . . .
49
Graph showing r o u n d n e s s v s . d i s t a n c e . . . . . . . .
. . .5 0
Graph showing s i z e v s . d i s t a n c e . . . . . . . . . . . . .
51
Panorama o v e r Cot to nw oo d v a l l e y . . . . .
........................ . . 54
U- sh a pe d v a l l e y o f Rock C r e e k .........................
59
M o ra i ne o f Sheep C r e e k G l a c i e r . . . . . . . . . .
i . . .
61
End m o r a i n e w e s t o f Duck C r e e k . .............................................................. 61
S t r i a t e d b o u l d e r n e a r Duck C r e e k . ..........................................................63
T y p i c a l k e t t l e and Icame t o p o g r a p h y i n t h e Duck C r e e k
Moraine. . . . . . . . . . .
................... . . . . . . . . .
63
Panorama sh owing l a t e r a l m o r a i n e o f Duck C r e e k G l a c i e r . . 64
P h y s i o g r a p h i c e x p r e s s i o n o f t h e o l d e s t o f t h e two
g l a c i a l moraines
........................ ....
6,5
P h y s io g ra p h ic e x p re s s io n o f e a r l y moraine . . .
..................... 66
R o c k - t e r r a c e a l o n g Rock C r e e k . . . . . . . . . . . . . .
72 .
View up Rock C r e e k . . . . . . . . . . . . . . . . . . . .
73
B r a i d i n g c h a n n e l o f Rock C r e e k . . . ..................................
73
P r o f i l e s a c r o s s Rock C r e e k v a l l e y and a d j o i n i n g s u r f a c e s . 76
P r o f i l e a c r o s s Rock C r e e k v a l l e y . . . . . . .
............................... 77
H y p o t h e t i c a l s e c t i o n showing d i f f i c u l t i e s e n c o u n t e r e d i n .
a s s i g n i n g an a g e t o a g r a v e l o u t c r o p ............................................79
Sample d a t a s h e e t u s e d i n s t a t i s t i c a l s t u d i e s . . . .
in pocket
ABSTRACT
S i g n i f i c a n t and i n t e r e s t i n g g e o m o r p h i c - g l a c i a l r e l a t i o n s a l o n g t h e
s o u t h w e s t m a r g i n o f t h e C r a z y M o u n ta i n s p r o v i d e d a t a f o r an u n d e r s t a n d i n g o f
a . s e r i e s o f l a t e C e n o z o i c s u r f a c e s . P a l e o c e n e ( F o r t Union) s a n d s t o n e s , i n t o
which s t o c k s , s i l l s and d i k e s h a v e been i n t r u d e d , c o m p r i s e t h e r e l a t i v e l y
homogeneous s e d i m e n t a r y s u c c e s s i o n u n d e r l y i n g t h e a r e a . The g e n t l y n o r t h e r l y
d i p p i n g b e ds do n o t g r e a t l y a f f e c t t h e g e o m o rp hol og y o f t h e a r e a .
F o u r s u r f a c e s y s t e m s , formed by l a t e r a l l y p l a n a t i n g s t r e a m s i s s u i n g from
th e Crazy Mountains, a r e o f th e f o llo w in g a g e s .
Surface
Surface
Surface
Surface
I -----I I -----I I I -----IV ------
e a rly P leisto cen e or la te Pliocene
e a r ly to m id -P leisto cen e
e a r l y W is c on s in
intra-W isconsin
G rav els, probably i n d i c a t i v e o f o l d e r s u rf a c e rem nants, a r e a lso p re se n t
on h i g h b e n c h e s ab ov e s u r f a c e I .
Although t h e p r e s e n t Yellow stone R iv e r flows
e a s t w a r d , t h e p r e s e n c e i n t h e G a l l a t i n V a l l e y o f g r a v e l s from t h e C r a z y
M o u n t a i n s , s u g g e s t s t h a t d r a i n a g e p r i o r t o t h e c u t t i n g o f s u r f a c e I was
d i r e c t e d westward.
In t h e n o r t h , e r o s i o n s i n c e t h e l a t e s t g l a c i a l a d v a n c e h a s bee n c o n f i n e d
t o d e e p , n a r r o w v a l l e y s , w h e r e as i n t h e s o u t h , wher e e r o s i o n has been more
e f f e c t i v e , v a l l e y s a r e wi d e and o n l y s m a l l r e m n a n t s o f t h e e a r l i e r s u r f a c e s
remain.
Ages o f t h e two y o u n g e s t s u r f a c e s w er e d e t e r m i n e d a f t e r a p p r a i s a l o f
t h e i r r e l a t i o n s h i p s w i t h g l a c i a l f e a t u r e s . Two s u b s t a g e s o f W i s c o n s i n g l a c i a ­
t i o n a r e r e c o g n i z e d ; t h e l a t e s t m o r a i n e i s f r e s h , t h e e a r l i e s t q u i t e su b d u e d .
They a r e e a s i l y d i s t i n g u i s h e d i n t h e f i e l d by c o m p a r i s o n .
C o n t r a r y t o A l d e n 1s (1932) b e l i e f , I ha v e c l a s s i f i e d s u r f a c e I I as
P l e i s t o c e n e and t h e r e f o r e y o u n g e r t h a n t h e F l a x v i l i e P l a i n as i t was d e f i n e d
in n o r t h e r n Montana.
S t a t i s t i c a l s t u d i e s i n d i c a t e i n c r e a s i n g s p h e r i c i t y and r o u n d n e s s and
d e c r e a s i n g s i z e w i t h t r a n s p o r t d i s t a n c e e x c e p t on t h e o l d e s t s u r f a c e .
The
s t u d i e s show t h a t t h e t h r e e y o u n g e r s u r f a c e s w er e s t r e a m - c a r v e d , b u t t h e
o l d e s t s u r f a c e has u n d e r g o n e m o d i f y i n g i n f l u e n c e s , due e i t h e r t o i t s g r e a t e r
a g e and l e n g t h o f e x p o s u r e o r r e w o r k i n g by g l a c i e r s .
EROSIONAL SURFACES AND GLACIAL GEOLOGY ALONG THE SOUTHWEST FLANK OF THE
CRAZY MOUNTAINS, MONTANA
INTRODUCTION
Location
The a r e a u n d e r t a k e n f o r s tti dy i s l o c a t e d i n n o r t h e a s t e r n P a r k C o u n t y ,
Montana, on t h e s o u t h w e s t e r n f l a n k o f t h e C r a z y M o u n t a i n s .
Approximate
l i m i t s o f t h e a r e a a r e hi ghway 89 on t h e w e s t , AO0Op1 N o r t h l a t i t u d e on t h e
north,
and t h e P a r k Co un ty l i n e on t h e e a s t .
The s o u t h e r n l i m i t l i e s a l o n g
an e a s t - w e s t l i n e a b o u t f o u r m i l e s n o r t h o f t h e Y e l l o w s t o n e R i v e r .
The
a r e a i n c l u d e s a b o u t 200 s q u a r e m i l e s b u t p a f t s o f i t r e c e i v e d much more
c o n c e n t r a t e d s tt id y t h a n o t h e r s .
P urposes o f T his Study
-
P r i m a r y p u r p o s e s o f t h e s t u d y w er e t h r e e f o l d .
One g o a l was t o d e ­
s c r i b e t h e g e o m or ph ol o gy o f t h e a r e a w i t h p a r t i c u l a r r e f e r e n c e t o t h e b r o a d ,
flat
e r o s i o n a l s u r f a c e s which hea d n e a r t h e m o u n t a i n s and e x t e n d w e s t w a rd
to th e Shields R iver.
A s e c o n d o b j e c t i v e was t o i n v e s t i g a t e t h e g l a c i a l
d e p o sits with p a r t i c u l a r a t t e n t i o n to le a rn in g the r e l a t i v e ages of th e s e
d e p o s i t s and t h e s u r f a c e s .
Finally,
an a t t e m p t was made t o l e a r n t h e man­
n e r i n which t h e p e d i m e n t - l i k e s u r f a c e s w er e formed an d,
i f possible,
to
extend th e s e fin d in g s to a gen eral understanding of th e p ro cesses respon­
s i b l e f o r pediment f o rm a tio n ,
e s p e c i a l l y i n a r e a s o f e s s e n t i a l l y homogeneous
lithology.
The m et h od s o f t h e s t u d y ,
deduction,
a s i d e from s i m p l e f i e l d o b s e r v a t i o n and
i ri d l u d e d t h e s t a t i s t i c a l a n a l y s e s o f 42 g r a v e l s a m p l e s c o l l e c t e d
in se le c te d l o c a l i t i e s .
Study o f th e bedrock,
i n s o f a r a s i t was p e r t i n e n t
2
t o t h e p r o j e c t , c o n t r i b u t e d t o a g r e a t e r u n d e rs ta n d in g o f t h e geomorphology.
The o v e r a l l t o p o g r a p h i c p a t t e r n i s one o f b r o a d ,
f a c e s which a r e b e i n g d e e p l y d i s s e c t e d by s t r e a m s ,
f l a t erosional sur­
Several gravel-capped
rem nants a r e a l l t h a t remain o f t h e s u r f a c e s in t h e s o u th e r n p a r t o f t h e
a r e a which h a s been more t h o r o u g h l y d i s s e c t e d t h a n t h e n o r t h e r n p a r t .
The
s u r f a c e s a r e i n t e r r u p t e d and s e p a r a t e d i n p l a c e s by l a r g e a s y m m e t r i c a l h i l l s
a nd r i d g e s wh ic h h a v e , w i t h few e x c e p t i o n s ,
ern s lo p e s .
Near t h e m o u n t a i n s ,
s t e e p s o u t h e r n and g e n t l e n o r t h ­
r e l i e f is co n sid e rab le ; th e t e r r a i n covered
by g l a c i a l d e p o s i t s i s v e r y hummocky.
The a r e a i s f l a n k e d by t h e t o w e r i n g s o u t h e r n C r a z y M o u n ta i n s which
r e a c h an e l e v a t i o n o f 1 1 ,2 1 4 f e e t .
In c o n t r a s t ,
t h e a r e a h a s e l e v a t i o n s a s low a s 4500 f e e t .
n o t a b l y Co tt o n w o o d C r e e k and Rock C r e e k ,
In p l a c e s ,
th e southw estern p a rt, of
Some o f t h e l a r g e r s t r e a m s ,
f l o w i n can y o n s o v e r 400 f e e t d e e p .
t h e s u b d u e d t o p o g r a p h y o f t h e mapped a r e a i s b r o k e n by
s m a l l d i k e s which s t a n d gb ove t h e g e n e r a l l a n d s c a p e ; n e a r t h e m o u n t a i n s
s e v e r a l d i k e s s t a n d as h i g h a s 40 f e e t a b o v e t h e s u r r o u n d i n g l a n d s c a p e .
The h i g h e r a r e a s a r e w e l l w a t e r e d ; t h e r e a r e hteavy snows i n w i n t e r
and f r e q u e n t sh ow er s i n summer,
some o f which a r e o f a c l o u d b u r s t n a t u r e .
C h a ra c te r o f v e g e ta tio n v a r ie s with e le v a ti o n ,
t h e lo w e r r e a c h e s b e i n g c o v ­
e r e d by g r a s s and s a g e , t h e h i g h e r by e v e r g r e e n t r e e s .
Areas o f moraine
a r e e x t e n s i v e l y f o r e s t e d w i t h t h i c k e v e r g r e e n gr ow th and i n some v a l l e y s
a s p e n and c o t t o n w o o d grow i n a b u n d a n c e .
Wheat i s r a i s e d on t h e lo we r s u r ­
f a c e s a nd a l f a l f a along, t h e S h i e l d s R i v e r i n i r r i g a t e d a r e a s .
3
Most d r a i n a g e s a r e d i r e c t e d s o u t h w e s t w a r d t o w a r d t h e S h i e l d s H i v e r
which i n t u r n f l o w s s o u t h e a s t i n t o t h e Y e l l o w s t o n e H i v e r , t h e r e g i o n a l mas­
t e r stream .
S everal small p e re n n ia l stream s a re s p rin g - fe d ,
b u t most a r e
f e d by s u r f a c e r u n o f f .
F i g u r e 2 . — I n d e x Map o f Montana
Previous
Investigations
In s p i t e o f a c c e s s i b i l i t y ,
g eo m o r p h i c i n v e s t i g a t i o n s i n t h e Cr a z y
M o u n ta i n s a r e a have been l i m i t e d .
Lewis and C l a r k p a s s e d t h e s o u t h e r n f o o t
o f t h e m o u n t a i n s i n 1806 and named t h e S h i e l d s H i v e r .
F. V. Hayden i n 1872
s p e a k s o f t h e d i s t a n t r a n g e ( h e c a l l e d them t h e "C razy Woman M o u n t a i n s " ) ,
and C a p t a i n L u d l o w ' s e x p e d i t i o n i n 1873 p a s s e d down t h e s o u t h f o r k o f t h e
M usselshell Hiver,
a t t h e n o r t h end o f t h e r a n g e ,
accom pa nyi ng g e o l o g i s t ,
where L. S. Dana, t h e
n o t e d t h e t h e r a l i t e s i l l s o f Comb C r e e k .
The f i r s t g e o l o g i c e x p l o r a t i o n was made i n 1883 by J . E. Wolff
4
working f o r t h e N orthern T r a n s c o n t in e n t a l Survey.
W o lf f ( 1 8 9 1 ,
1938) pub?-
I i s h e d two p a p e r s o f a g e n e r a l n a t u r e on t h e C r a z y M o u n ta i n s b o t h p r i m a r i l y
concerned w ith th e igneous rocks o f th e a r e a .
by J . P.
W a l t e r H„ Weed, ac co m p a n ie d
I d d i n g s and L„ y., P i r s s o n , made t r i p s i n 1890 and 1895 f o r t h e
United S t a t e s G eological Survey.
T h e s e w o r k e r s d e s c r i b e d t h e a r e a l and
s t r u c t u r a l g e o l o g y o f t h e L i v i n g s t o n and L i t t l e B e l t M o u n ta i n s a r e a s ( I d d i n g
and Weed,
1894; Weed,
1899).
G0 Re M a n s f i e l d ( 1 909 ) p u b l i s h e d a b r i e f p a p e r o f a g e n e r a l n a t u r e
on g l a c i a t i o n i n t h e C r a z y M o u n t a i n s .
Of i n t e r e s t t o o ,
i s A l d e n 1S (1932)
V'-. •
p a p e r on t h e p h y s i o g r a p h y and g l a c i a l g e o l o g y o f e a s t e r n Montana which
t r e a ts b r ie f ly of the area.
Very l i t t l e work h a s been done i n r e c e n t y e a r s . i n . t h e . Cr a z y ,, M ou n ta in s ..
v i c i n i t y . and a l t h o u g h t h e B i l l i n g s G e o l o g i c a l S o c i e t y did. c o n d u c t a , , f i e l d ..
c o n f e r e n c e , i n t h e C r a z y M ou n tai n B a s i n i n 1957, v e r y l i t t l e , o f. .. th is was.
.
c o n c e r n e d w i t h t h e ge om or ph o lo g y o f t h e a r e a .
S i n c e r e a p p r e c i a t i o n i s e x t e n d e d t o Dr. Jo h n de l a . Montague ..for ,,his.
g e n u i n e i n t e r e s t a nd g u i d a n c e d u r i n g t h e p r e p a r a t i o n o f t h i s t h e s i s .
Dr.
W; J . McMannis a i d e d m a t e r i a l l y by h i s t i m e l y s u g g e s t i o n s and i n s t r u c t i o n .
Thanks a r e due a l s o t o D r s . C 6 C-. B r a d l e y , N i c h o l a s H e l b u r n , R. A 0 C h a d w ic k 6
and Mr. M. J . E d i e , o f t h e D e p a r tm e n t o f E a r t h S c i e n c e s a t Montana S t a t e
C ollege.
The D e p a r t m e n t o f E a r t h S c i e n c e s s u p p l i e d f i e l d e q u ip m e n t f o r t h e
study.
I am i n d e b t e d t o M e s s r s . B i l l and Ed Eyman f o r p r o v i d i n g s u i t a b l e
5
ca mping .g r o u n d s and s h e l t e r d u r i n g i n c l e m e n t w e a t h e r a s w e l l a s i n v a l u a b l e
a d v i c e on l o c a l r o a d s .
REGIONAL GEOLOGY
Introduction
,The C r a z y M o u n t a i n s ,
s o u t h e r n m o s t and h i g h e s t o f s e v e r a l , c o n s a n g u i n e .
egus. i s o l a t e d m o u n ta in , m a s s e s e x t e n d i n g t h r o u g h c e n t r a l Montana n o r t h w a r d
n e a r l y , to, , t h e . C a n a d i a n b o u n d a r y ,
l i e between, t h e m e r i d i a n s o f 1.10? 1 5 ' ,and,..
11G045" West , l o n g i t u d e , , and p a r a l l e l s o f ' 4 5 045" and 4 6 ? 3 0 ' N o r t h l a t i t u d e . .
The g e n e r a l t r e n d i s a l i t t l e w e s t o f n o r t h ,
and t h e i r w i d t h .25 m i l e s .
whose s t r u c t u r e ,
t h e i r length, about 4 5 .m ile s , .
They a r e a c l u s t e r o f h i g h . a n d r u g g e d ..peaks,,
t o g e t h e r w i t h t h e un u s u a l, l i m e - a l k a l i c . c h a r a c t e r , o f the,
i g n e o u s r o c k s and t h e m a g n i f i c e n t e x p o s u r e s , gi ve. t h e m . g e o l o g i c , i n t e r e s t s
B e d r oc k c o n s i s t s o f s a n d s t o n e s and s h a l e s o f l a t e . C r e t a c e o u s , to. P a l e o c e n e
a g e i n t o wh ic h t h r e e c o r e s o f i g n e o u s r o c k o f E o c e n e a g e h a v e been, i n j e c t e d
a c co m p a n ie d by t h o u s a n d s . o f a s s o c i a t e d l a c c o l i t h s ,
s i l l s and d i k e s .
Stratigraphy
Most o f t h e s e d i m e n t a r y r o c k s e x p o s e d i n t h e a r e a a r e o f P a l e o c e n e
( F o r t Union) a g e , a n d c o m p r i s e t h e u p p e r p a r t o f t h e L i v i n g s t o n f o r m a t i o n
w hi ch i s w i d e l y d i s t r i b u t e d t h r o u g h o u t t h e C r a z y Mo un tai n B a s i n .
The L i v ­
i n g s t o n f o r m a t i o n c o n s i s t s o f a n d e s i t i c s a n d s t o n e s and s h a l e s o f l a t e
Cretaceous to Paleocene age.
Some w r i t e r s p r e f e r t o r e s t r i c t t h e . L i v i n g ­
s t o n r o c k s t o t h e l a t e s t C r e t a c e o u s and c a l l t h e P a l e o c e n e p a r t F o r t Un io n.
McMannis (1 95 5 ) mapped t h e t o p o f t h e H e l l C r e e k member o f t h e L i v i n g s t o n
f o rm a tio n s e v e r a l m ile s west o f t h e S h i e ld s R iv e r and c o n s i d e r e d e v e ry th in g
6
to the ea st of t h i s
l i n e t o be o f P a i e o c e n e a g e ( s e e F i g u r e 2 ) „
The H e l l
C r e e k i s t h e u p p e r m o s t C r e t a c e o u s member o f t h e L i v i n g s t o n f o r m a t i o n .
A c c o r d i n g t o W olf f ( 1 9 3 8 ) , m a s s i v e s a n d s t o n e s a n d some s h a l e s g e n e r ­
a l l y p r e d o m i n a t e w e s t o f t h e C r a z y M o u n ta i n s b u t i n t h e m o u n t a i n s t h e s e g i v e
way t o s h a l e s i h t e r b e d d e d w i t h a few t h i n l i m e s t o n e s .
Sandstones o f th e
l o w e r a r e a n e a r t h e S h i e l d s R i v e r a r e a n d e s i t i c b u t t h e y become l e s s so
toward th e e a s t .
The r o c k s a r e m o s t l y m e d i u m - g r a i n e d d r a b , o l i v e - g r a y to..
yellow , tu ffa c e o u s to a rk o s ic sandstones.
C la s tic c o n stitu e n ts are q u ite
v a r i a b l e c o n s i s t i n g o f a n g u l a r to s u b - a n g u l a r f r a g m e n t s o f q u a r t z , m i c r o ­
cline,
orthoclasq,
posed b i o t i t e ,
s o d i c t o c a l c i c p l a g i o c l a s e and a few g r a i n s o f decom­
h o r n b l e n d e and a u g i t e a s w e l l a s a c c e s s o r y m in e r a l s ,, .
Honnded
f r a g m e n t s o f l i m e s t o n e a r e commonly f o u n d i n t e r b e d d e d and in; p l a c e s , c a r ­
bonate f i l l s
i n t e r s t i c e s and r e p l a c e s c l a s t i c g r a i n s .
be d o f c o n g l o m e r a t e ,
25 f e e t t h i c k ,
interbedded in the sandstones.
rocks,
ba n de d f l i n t y s l a t e ,
W o lf f (.1938)..f o u n d a
a t t h e e x t r e m e hea d o f Cot to nw oo d Creek,
The p e b b l e s a r e q u a r t z ,
p o r p h y r i t I c .,,igneous
q u a r t z i t e and a c r i n o i d a l l i m e s t o n e .of. C a r b o n i f ­
erous age.
Structure
An a s y m m e t r i c sync l i n e i n v o l v i n g t h e y o u n g e s t ( F o r t Onion) beds and
tr e n d in g n o r t h e a s t p a s se s j u s t south o f W i l s a l l .
th e southeast,
g en tle flank of t h is
The mapped a r e a l i e s on
s y n c l i n e whi ch c a u s e s t h e F o r t Union
b e d s t o d i p n o r t h w e s t a t a n g l e s o f from 5° t o 1 5 ° .
The n o r t h w e s t f l a n k o f
th e sy n clin e is v e r t i c a l to overturned.
S t r u c t u r e h as n o t bee n o f p a r a m o u n t i m p o r t a n c e i n f a s h i o n i n g t h e p r e ­
sent landscape,
b u t i t h a s c o n t r i b u t e d i n v a r i o u s ways.
In t h e c e n t r a l p a r t
7
CLYDE
PARK
F i g u r e 3 . — Wajor t e c t o n i c f e a t u r e s n e a r t h e C r a z y M o u n ta in s
of the range,
erous,
sills
i n and n e a r t h e d i o r i t e s t o c k ,
v e r t i c a l d i k e s a r e v e r y num­
b u t t h e y d e c r e a s e i n number w e s t w a rd t o w a r d t h e f o o t h i l l s ,
re m a in a b u n d a n t .
w h e r e as
E v i d e n t l y magma was f o r c e d l a t e r a l l y p a r a l l e l t o
t h e u p l i f t e d and domed s t r a t a a s s o c i a t e d w i t h t h e d i o r i t e s t o c k , where
r a d i a l t e n s i o n p r o d u c e d by t h e u p l i f t o f t h e s t o c k form ed c r a c k s t h a t a l ­
lowed t h e i n t r u s i o n o f d i k e s .
N o t a b l e e x a m p le s o f s i l l s which f i t
d e s c r i p t i o n i n c l u d e Sheep M ountain j u s t s o u t h o f t h e mapped a r e a ,
this
and Ibex
8
M ou nt a in ( X h e r a l i t e B u t t e ) on t h e n o r t h end o f t h e a r e a .
Both s i l l s
dip
northward a t a n g les comparable to th e dip o f th e surrounding sedim ents,
Xhe
n o r t h e r l y d i p i s a l s o i m p o r t a n t i n t h a t i t commonly d e t e r m i n e s , the. s h a p e o f
the v alley s,
th e south,
t h e n o r t h s i d e s h a v i n g a d e c i d e d t e n d e n c y t o be s t e e p e r t h a n
as,
f o r e xa m pl e, much o f t h e v a l l e y o f Cot to nw oo d C r e e k ,
The C r a z y M o un ta in s a r e n o t a f o l d e d r a n g e b u t r a t h e r t h e p r o d u c t o f
d i f f e r e n t i a l e r o s i o n o f i g n e o u s i n t r u s i o n s and p r e e x i s t i n g g e n t l y d i p p i n g
sedim ents.
The a r e a o c c u p i e d by t h e r a n g e i s a s h a l l o w b a s i n s t r u c t u r e
whic h h a s b e e n m o d i f i e d by d om e-s ha ped u p l i f t s o f which t h e most marked i s
t h a t connected with th e c e n t r a l d i o r i t i c s to c k ,
from whi ch t h e s t r a t i f i e d
r o c k s d i p away a t d e c r e a s i n g a n g l e s .
A c c o r d i n g t o W o lf f ( 1 9 3 8 ) , most o f t h e r a d i a l , s t r e a m s ,
s o u th e r n p a r t o f th e r a n g e has r a d i a l d r a i n a g e ) ,
(the e n tire
hav e w a t e r f a l l s , and c l i f f s
a t a c e r t a i n d i s t a n c e from t h e c e n t r a l p a r t o f t h e r a n g e .
Above this., " f a l l -
l i n e " t h e v a l l e y s a g a i n wi den and t h e s t r e a m s haVe a somewhat more g e n t l e ,
slope to th e head.
T h i s " f a l l - l i n e " i s due t o t h e l o c a l h a r d e n i n g o f t h e .
s e d i m e n t a r y r o c k s p r o d u c e d by t h e c e n t r a l d i o r i t i c . s t o c k .
W o lf f w r o t e t h a t t h e h a r d e n i n g e f f e c t p r o d u c e d by t h e i n t r u s i o n o f
t h e Eocene magmas c o u p l e d w i t h t h e honeycombing o f t h e s o f t s t r a t a by d i k e s
t o p r o d u c e a fra mework which h o l d s t h e s e d i m e n t s t o g e t h e r e n a b l e d t h e w h o le
mass t o r e s i s t t h e e r o s i o n which l e v e l e d t h e a d j o i n i n g c o u n t r y ,
teristic
w hi ch makes t h e r a n g e u n i q u e i n t h i s a r e a .
a charac­
V -
9
LIST OF MAJOR CONCLUSIONS
Xhe f o l l o w i n g c o n c l u s i o n s a r e d e v e l o p e d i n d e t a i l t h r o u g h o u t t h e body
o f t h i s t h e s i s and i n t h e summary a t t h e e n d .
1.
F o u r m a j o r s u r f a c e s ha ve be e n form ed s o u t h w e s t o f t h e C r a z y M o u n t a i n s .
The a g e s o f t h e s e s u r f a c e s a r e ,
from o l d e s t t o y o u n g e s t ;
l ) .early Pleistocene
o r p o s s i b l e l a t e P l i o c e n e ; 2) mid t o l a t e P l e i s t o c e n e ; . 3) l a t e P l e i s t o c e n e ,
p r o b a b l y p r e - W i s c o n s i n g l a c i a l s t a g e ; and 4) l a t e P l e i s t o c e n e ,
consin g l a c i a l s ta g e .
some a r e a s ,
2.
intra-W is­
The p r e s e n t t i m e i s one o f d o m in a n t d o w n c u t t i n g in
l a t e r a l p la n a tio n in o t h e r s .
'
.
A l l t h e m a j o r s u r f a c e s w er e f orm ed by l a t e r a l l y c u t t i n g s t r e a m s .
An
i n s i g h t i n t o how t h e s u r f a c e s were form ed c a n be g a i n e d by s t u d y i n g Rock
■■
G r e e k which i s p r e s e n t l y i n t h e p r o c e s s o f w i d e n i n g i t s f l o o d p l a i n by l a t ­
.•
•
eral planation.
3.
T h e r e h a v e been a t l e a s t two s e p a r a t e l a t e P l e i s t o c e n e s u b s t a g e s o f
g l a c i a l a c t i v i t y in th e Crazy M ountains.
4.
G lacial re la tio n sh ip s,
y
o l d e r m o r a i n e l y i n g on t h e s e c o n d o l d e s t s u r f a c e
a nd y o u n g e r m o r a i n e l y i n g on t h e y o u n g e s t s u r f a c e , i n d i c a t e t h a t a t l e a s t
;
one and p o s s i b l y two o f t h e s u r f a c e s were c a r v e d d u r i n g i n t e r g l a c i a l s t a g e s .
5»
The s e c o n d o l d e s t s u r f a c e i n t h e a r e a ( s u r f a c e I I o f t h i s t h e s i s ) , which
h a s be e n d e s i g n a t e d t h e F l a x v i l l e P l a i n by p r e v i o u s w r i t e r s i s ,
younger than th e F l a x v i l l e P l a i n .
the F la x v ille Plain e ith e r .
in r e a l i t y ,
Surface I (th e o ld e s t surface)
is not
E ith e r th e F l a x v il le P la in is not rep re sen te d
'
'
'
I
M -
1
(
10
i n t h i s atfea o r i t h a s b e e n m i s - d a t e d i n o t h e r a r e a s ,
or perhaps, both of
these p o s s ib i li ti e s are tru e ,
6,
A l t h o u g h t h e o l d e s t o b s e r v e d s u r f a c e , a s r e v e a l e d by t h e s t a t i s t i c a l
studies,
i s c o v e r e d by g r a v e l s o f d i f f e r i n g c h a r a c t e r t h a n . t h e o t h e r t h r e e
surfaces,
about a l l t h a t can be s a id w ith c e r t a i n t y a b o u t.th a t, s u r f a c e i s
that i t
i s o ld e r than the o th e r s u rf a c e s .
In terp retatio n .o f.th e s ta tis tic a l
d a t a shows t h a t su ch s t u d i e s c a n be e x t r e m e l y u s e f u l . i n . a n a l y z i n g t h e e r o s i o n a l h i s t o r y o f an a r e a .
The t a s k o f c o r r e l a t i n g s u r f a c e s c a n be a i d e d
by s uc h s t a t i s t i c a l s t u d i e s ,
PROMINENT IRREGULAR TOPOGRAPHIC FEATURES
P r o m i n e n t h i l l s d o m i n a t e some i n t e r s t r e a m d r e a s ,
Most i m p o r t a n t o f
t h e s e a r e I b e x M ou n ta in C T h e r a l i t e B u t t e ) , C e d a r and R a t t l e s n a k e B u t t e s ,
E l k M ou nt ai n and Cho se H i l l ( s e e F i g u r e I ) .
L e s s p r o m i n e n t a r e Squa w's
T i t , A n t e l o p e B u t t e and C h o k e - t o - D e a t h B u t t e a s w e l l a s numerous d i k e f orm ed r i d g e s .
I b e x M o u n ta i n , C e d a r B u t t e and R a t t l e s n a k e R i d g e ,
Mou nta in t o t h e s o u t h o f t h e a r e a ,
a s w e l l as Sheep
a re s i l l s o f t h e r a l i t i c to d i o r i t i c rock
which h a v e b e e n i n t r u d e d i n t o g e n t l y n o r t h e r l y - d i p p i n g s e d i m e n t a r y s t r a t a ,
W ol ff (193 8) h as p o i n t e d o u t t h a t t h e more e x t e n s i v e j o i n t i n g n e a r e r t h e
m ountains has fa v o re d t h e i n t r u s i o n o f d ik e s whereas t h e l e s s e x t e n s i v e l y
j o i n t e d s e d i m e n t s f u r t h e r away from t h e main m ou n ta in r a n g e h a s f a v o r e d t h e
e mp la cem en t o f s i l l s b e tw e e n t h e l a y e r s o f r o c k s .
A l l t h e s e f e a t u r e s hav e
s t e e p s o u t h e r n s l o p e s and more g e n t l e n o r t h e r l y o n e s .
This c h a r a c t e r i s t i c
c a n be a t t r i b u t e d t o t h e n o r t h e r l y d i p p i n g F o r t Union s e d i m e n t s i n t o which
11
Figure 4.
View n o r t h w e s t o v e r I b e x M ountain from s u r f a c e
s l o p e s a r e a c t i v e a nd c o v e r e d w i t h c o l u v i u m e s p e c i a l l y on
(A).
N o t i c e t h e l a r g e d i k e e x t e n d i n g s o u t h from C t o B.
t r u n c a t e d by e r o s i o n a t B b u t i t c o n t i n u e s t o t h e l e f t o f
III.
Xhe s o u t h
t h e u p pe r p a r t s
The o u t c r o p i s
the p ic tu r e .
F ig u re 5.
Dike s o u t h o f t h e Duck C r e e k m o r a i n e i n t h e e x tr e m e e a s t e r n p a r t o f t h e
a r e a . T h i s d i k e o u t c r o p i s a b o u t 30 f e e t h i g h and 80 y a r d s l o n g .
Several s im ila r
d i k e s o f s m a l l e r s i z e a r e p r e s e n t t o t h e s o u t h w e s t i n t h e a r e a e a s t o f F a l l s C re ek
Ca ny o n.
I-*
GJ
ill
F i g u r e 6.
View e a s t up F a l l s C r e e k C a n y o n . The r i d g e on t h e l e f t i s t h e r e l a t i v e l y n a r r o w d i k e
shown i n F i g u r e 7,
Sout h o f t h e canyon t h e d i k e wide ns o u t e v e n t u a l l y i n t o C e d a r B u t t e .
14
t h e s i l l s we re e m p l a c e d .
E r o s i o n h a s s i n c e form ed t h e p r o m i n e n t s c a r p s on
Ih e southern s id e s .
Several large dikes,
as w e l l a s i n n u m e r a b l e s m a l l e r o n e s , a r e p r e s e n t ,
some o f t h e l a r g e s t o n e s a p p a r e n t l y h a v i n g s e r v e d a s f e e d e r d i k e s f o r t h e
sills.
Of p a r t i c u l a r i n t e r e s t
is
the la r g e d ike n o rth of Cedar B utte
which i s t r a n s e c t e d by F a l l s C r e e k ( F i g u r e 6 ) .
on t h e d i k e ,
F a l l s Creek i s superimposed
and i t s c an yon c u t due w e s t t h r o u g h t h e d i k e s u g g e s t s c o n s i d e r ­
a b l e c h a n g e i n d r a i n a g e d i r e c t i o n s i n c e s u p e r p o s i t i o n b e c a u s e b o t h above
and be low t h e ca nyon t h e s t r e a m has a d e f i n i t e s o u t h w e s t e r l y c o u r s e .
F ig u re 7. Topographic e x p re s s io n o f d i o r i t i c d ik e
north of F a l ls Creek.
View n o r t h - n o r t h e a s t a l o n g t h e
r i d g e t o l e f t o f F a l l s C r e e k Canyon shown i n F i g u r e 6 .
15
Other r e l a t i v e l y high h i l l s
and A n t e l o p e B u t t e ,
s u c h as Ghpse H i l l , C h o k e .- to - D e a th B u t t e ,
e x i s t b e c au se o f t h e i r capping o f g r a v e l ( s e e F ig u re I)
The f l a t t o p s o f t h e s e t h r e e h i l l s a r e a l l r e m n a n t s o f a s u r f a c e ( s u r f a c e
I I o f t h i s t h e s i s ) which was o n c e much more e x t e n s i v e t h a n i t i s a t t h e
p resen t tim e.
Th e se h i l l s
hav e r e l a t i v e l y s t e e p s o u t h e r n s c a r p s l o p e s ,
a
c o n s e q u e n c e Of t h e n o r t h e r l y d i p o f t h e F o r t Union s e d i m e n t s o f which t h e y
a r e co mp os ed .
D r a i n a g e a r o u n d C h o k e - t o - D e a t h and A n t e l o p e B u t t e s i s r a d i a l
E l k M ou n ta i n ( s e e F i g u r e I ) ,
a sso c ia te d with i t ,
s t a n d s up by v i r t u e o f a g r a v e l c a p , mo st o f which has
o n l y r e c e n t l y b e e n re m o v e d .
of this th esis),
a l t h o u g h i t h as a s m a l l i g n e o u s i n t r u s i o n
I t was o n c e p a r t o f a h i g h s u r f a c e ( s u r f a c e I
and was i s o l a t e d a s t h e s u r f a c e was r em ov e d.
Squaw's T i t ( s e e F ig u re 8 ),
two m i l e s n o r t h e a s t o f C l y d e P a r k , was
i n c o r r e c t l y mapped by W o lf f (193 8) a s a T e r t i a r y i n t r u s i o n and a l t h o u g h
t h e r e i s o ne s m a l l d i k e on t h e s i d e o f t h e h i l l t h e main mass i s se d im e n ­
tary.
I t i s d o u b t f u l w h e t h e r W olff had t h i s d i k e i n mind when he drew h i s
map b e c a u s e s e v e r a l l a r g e r d i k e s n o t o v e r a m i l e away w er e i g n o r e d .
seems p r o b a b l e t h a t S q u a w 's T i t ,
intrusion,
It
i n s t e a d o f being p r i m a r i l y a T e r t i a r y
i s an a r e a o f r o c k s more r e s i s t a n t t h a n t h o s e o f t h e s u r r o u n d i n g
countryside.
P a rtic u la rly in te re s tin g are the in ten sely tw isted fin e ­
g r a i n e d s i l t s t o n e s on t h e h i l l which a p p e a r t o hav e bee n c o n t o r t e d by
s l i d i n g along th e bedding p la n e s w h ile s t i l l
in a p l a s t i c s t a t e .
Perhaps
t h e c o r r u g a t e d e f f e c t c r e a t e s a r o c k r e s i s t a n t enough t o a c c o u n t f o r t h e
superior elevation.
C r a z y M o un ta in b a s i n ,
T h i s same t y p e o f s t r u c t u r e i s common i n much o f t h e
ho wev er , and i n many p l a c e s i t i s h o t a s s o c i a t e d
w i t h h i g h s t a n d i n g t e r r a i n f e a t u r e s . . ,Some s u b t l e c h a n g e s a s a r e s u l t o f
16
b a k i n g o f t h e s e d i m e n t s by t h e d i k e may a c c o u n t f o r t h e h a r d n e s s , b u t i f s o,
they a re not a p p a re n t.
Figure 0.
Squaw1s l i t from t h e n o r t h a t a d i s t a n c e
o f a b o u t one m i l e .
B e a r t o o t h M o u n ta i n s a r e i n t h e
fa r distance.
SURFACES SOUXHWESf OF XHE MOUNTAINS
Introduction
The f l a t ,
smooth b e n c h e s which s l o p e away from t h e m o u n t a i n s a r e
veneered with g r a v e l .
ed down so t h a t i t
moved.
Be d ro c k b e n e a t h t h e g r a v e l has bee n u n i f o r m l y sm o ot h ­
i s seldom e x p o s e d e x c e p t wher e t h e g r a v e l h as been r e ­
In t h i s t h e s i s , t h e s e f l a t b e n c h e s a r e r e f e r r e d
P r i m a r i l y on t h e b a s i s o f e l e v a t i o n s ,
in a d d itio n
to a s " s u r f a c e s " .
f o u r s e p a r a t e s u r f a c e s y s te m s
to t h e p r e s e n t r i v e r f l o o d p l a i n s hav e bee n d i s t i n g u i s h e d s o u t h ­
west o f th e Crazy M ountains.
Each s u r f a c e c o u l d be d i v i d e d i n t o s u b s u r f a c e s ,
17
but,
i n s o f a r a s i t was f e a s i b l e ,
grouped t o g e t h e r .
youngest.
t h e s e v a r i o u s e p i c y c l i c s u r f a c e s w er e
The s u r f a c e s a r e numbered c o n s e c u t i v e l y f ro m o l d e s t t o
G r a v e l s old eir t h a n t h o s e on s u r f a c e I a r e r e s t r i c t e d t o n a r r o w
h ig h er r id g e s in th e m ountains.
These remnants a re p r e s e n t a t v arying
e l e v a t i o n s from 7200 f e e t up t o 1 1 , 0 0 0 f e e t .
i s very im portant because i t
surface I.
tic,
The e x i s t e n c e o f t h e s e g r a v e l s
shows t h a t s u r f a c e s were p r o d u c e d even b e f o r e
G r a v e l f r a g m e n t s on t h e s e r i d g e s a r e m o s t l y q u i t e l a r g e ,
diori-
t h o r o u g h l y w e a t h e r e d c o b b l e s which h a v e u n d e r g o n e e x t e n s i v e f r o s t
action.
Some o f t h e r o u n d i n g may be a p r o d u c t o f t h i s f r o s t a c t i o n .
G r a v e l s a m p l e s were t a k e n a t s e v e r a l l o c a t i o n s on e a c h s u r f a c e .
The
r e s u l t s o f t h e s t u d i e s o f t h e s e s a m p l e s a r e i n c l u d e d a t t h e end o f t h e d i s ­
cussion of the su rfaces.
sphericity,
roundness,
Fo u r g r a p h s hav e bee n p r e p a r e d t o show how t h e
s i z e and c o m p o s i t i o n o f t h e g r a v e l s v a r i e s w i t h
transport distance.
Surface I
S urface I,
h i g h e s t a nd o l d e s t s u r f a c e o f c o n s e q u e n c e i n t h e a r e a
s o u t h w e s t o f t h e C r a z y M o u n ta i n s i s p r e s e r v e d b e s t a l o n g t h e m o u n ta in f r o n t
and i n r e l a t i v e l y n a r r o w r i d g e s o n e - h a l f m i l e o r l e s s i n w i d t h e x t e n d i n g
g e n e r a l l y s o u t h w e s t w a r d from t h e m o u n t a i n f r o n t ( s e e F i g u r e l ) .
v a t i o n r a n g e s b e tw e en 6200 f e e t and 7200 f e e t „
Its e le­
A l t h o u g h s e v e r a l s m a l l rem­
n a n ts o f s u r f a c e I a r e p r e s e r v e d in t h e v i c i n i t y o f t h e mountain f r o n t ,
only
t h r e e a r e o f any a p p r e c i a b l e e x t e n t and t h e t o t a l a r e a o f t h e s y s te m o f
s u rfa c e s a ssig n e d to " su rfa c e I" i s not la r g e ,
m iles.
a b o u t two and o n e - h a l f s q u a r e
Except f o r ve ry n e a r t h e mountain f r o n t ,
wher e i t i s
steeper,
the
18
s l o p e a v e r a g e s a b o u t 250 f e e t p e r m i l e .
In s e c t i o n s 3, 4, and 5 o f T„ 2 N., E. 11 E . ,
th e r e i s a m oderately
w e l l - d e v e l o p e d j u n c t u r e b e tw e e n t h e s u r f a c e and t h e m o u n t a i n f r o n t ,
other areas i t
t e n d s t o be o b s c u r e d by g l a c i a l m o r a i n e .
t h i s ju n c tu r e p a r t i c u l a r l y sharp,
but in
At no p l a c e i s
a c o n d i t i o n p r o b a b l y c a u s e d by t h e c o n ­
s i d e r a b l e age o f t h e s u r f a c e r a t h e r t h a n i n i t i a l c o n d i t i o n s when t h e s u r ­
f a c e was i n t h e p r o c e s s o f b e i n g c u t .
M e c h a n i c a l w e a t h e r i n g o f t h e moun­
t a i n s l o p e s h a s c o v e r e d t h e h i g h e s t r e a c h e s o f t h e s u r f a c e w i t h t a l u s and
th e r e b y c r e a t e d t h e p r e s e n t rounded j u n c t u r e .
The c o m p o s i t i o n ,
sphericity,
s i z i n g and r o u n d n e s s o f t h e g r a v e l
c o b b l e s t h a t c a p s u r f a c e I d i f f e r s i g n i f i c a n t l y from t h o s e t h a t ca p t h e
o th e r major s u r f a c e s .
The a v e r a g e maximum d i a m e t e r o f t h e p a r t i c l e s a n a ­
l y z e d t e n d s t o i n c r e a s e away from t h e m o u n ta in f r o n t .
fo r surface II,
(see Figure 26).
roundness,
b u t t h e t e n d e n c y i s n o t q u i t e so c l e a r c u t
Of i n t e r e s t t o o ,
i s t h e f a c t t h a t b o t h s p h e r i c i t y and
e x p l a i n e d on p a g e s 43 and 44, d e c r e a s e w i t h d i s t a n c e from t h e
mountain f r o n t .
surfaces.
th e next o ld e s t,
This i s a ls o t r u e
The . o p p o s i t e i s t r u e f o r e a c h o f t h e o t h e r t h r e e m a j o r
Finally,
th e p e rc e n ta g e of igneous cobbles (igneous cobbles p lu s
s e d i m e n t a r y c o b b l e s e q u a l s 100%) i n c r e a s e s w i t h d i s t a n c e from t h e m o u n t a i n s ,
again in complete disagreem ent with data f o r th e o th e r s u r f a c e s .
As was p o i n t e d o u t on p a g e 8, t h e C r a z y M o u n ta i n s w er e p r o d u c e d by
d i f f e r e n t i a l e r o s i o n o f t h e e a s i l y removed F o r t Union s e d i m e n t s from t h e
s k e l e t o n - l i k e fram ewo rk o f d i o r i t e which h a r d e n e d t h e s e d i m e n t s and a i d s i n
h o l d i n g them t o g e t h e r .
In itially ,
when e r o s i o n b e g a n , t h e p e r c e n t a g e o f
F o r t Union r o c k s mu st ha ve b e e n much g r e a t e r t h a n i t
i s now b e c a u s e t h e
19
F i g u r e 9 . C e n t e r o f s u r f a c e I i n s e c t i o n 7, f . 2 N . ,
H. 11 F . , w e s t o f Sheep C r e e k .
Notice the angular
c h a r a c te r of the d i o r i t e b o u ld ers.
d i k e s which s t a n d a s r i d g e s t o d a y were o r i g i n a l l y i n t r u d e d i n t o l a y e r e d
sequences o f sedim entary ro ck .
I he p e r c e n t a g e o f F o r t Union i n t h e g r a v e l s
would be e x p e c t e d t o d r o p s t e a d i l y a s more o f t h e i g n e o u s comp le x became
e x p o s e d and c o r r e s p o n d i n g l y more i g n e o u s m a t e r i a l would a p p e a r i n g r a v e l s
on s u c c e s s i v e l y y o u n g e r s u r f a c e s ,
wh er e i t
i'his,
in f a c t ,
i s b o r n e o u t by F i g u r e 24
i s s e e n t h a t t h e c u r v e s do hav e a t e n d e n c y t o s h i f t
"upward" f a v o r ­
i n g i g n e o u s r o c k s more and more w i t h e a c h s u c c e s s i v e s u r f a c e .
O b s e r v a t i o n s o f t h e g r a v e l s b e i n g t r a n s p o r t e d by t h e p r e s e n t s t r e a m s
i n d ic a te t h a t the d i o r i t i c
sedim entary r o c k s .
r o c k s hav e a t e n d e n c y t o e n d u r e l o n g e r t h a n t h e
T h i s s u g g e s t s t h a t t h e o l d e r s u r f a c e s s h o u l d have more
d i o r i t i c m a t e r i a l on them t h a n t h e y o u n g e r s u r f a c e s b e c a u s e t h e s e d i m e n t a r y
20
F i g u r e 10. G r a v e l c o v e r w e s t o f Sheep C r e e k n e a r t h e
l o w e r end o f s u r f a c e I i n s e c t i o n 7, f . 2 N., R. 11 E . ,
looking so u th .
T h i s i s on t h e w e s t e r n l o b e o f t h e
surface.
r o c k s would be e x p e c t e d t o w e a t h e r away.
exist,
the tendency f o r d i o r i t i c
B e c a u s e t h e s e c o n d i t i o n s do n o t
r o c k s t o become more a b u n d a n t due t o d i f ­
f e r e n t i a l e r o s i o n must be s t r o n g e r t h a n t h e t e n d e n c y f o r t h e s e d i m e n t a r y
rocks to weather f a s t e r than the d i o r i t i c rocks a f t e r d e p o s it io n .
F i g u r e 11 f o r an i l l u s t r a t i o n o f t h e s e c o n d i t i o n s .
See
Separate observations
f o r e ach o f t h e two m a j o r r o c k t y p e s i n d i c a t e s t h a t c r y s t a l l i n e r o c k s hav e
h i g h e r v a l u e s f o r s p h e r i c i t y and mean s i z e ( s e e Appe nd ix A ).
The i n c r e a s e i n s i z e w i t h d i s t a n c e from t h e m o u n t a i n s c o u l d be e x ­
p l a i n e d i n t h e f o l l o w i n g m an n e r .
The c r y s t a l l i n e r o c k s a r e more r e s i s t a n t
and r e t a i n t h e i r s i z e more r e a d i l y t h a n t h e F o r t Union s e d i m e n t s , b o t h u n d e r
c o n d i t i o n s o f t r a n s p o r t a nd a f t e r d e p o s i t i o n and w e a t h e r i n g .
Because the
>
21
F i g u r e 11. S c h e m a t i c i l l u s t r a t i o n showing how t h e amount o f c r y s t a l l i n e
m a t e r i a l b e i n g removed from t h e m o u n t a i n s i n c r e a s e s w i t h t i m e .
c r y s t a l l i n e rocks c o n s t i t u t e in c r e a s in g ly larg e percentages of the t o t a l
g r a v e l c o v e r w i t h d i s t a n c e from t h e m o u n t a i n f r o n t ,
the t o t a l gravel cover
would be e x p e c t e d t o c o n s i s t o f an i n c r e a s i n g p e r c e n t a g e o f l a r g e p a r t i c l e s
f u r t h e r from t h e m o u n t a i n f r o n t t h a n n e a r i t .
o f F o r t Union s e d i m e n t s n e a r t h e m o u n t a i n s h a s ,
The i n i t i a l p r e p o n d e r a n c e
i n t i m e , w e a t h e r e d more
than the c r y s t a l l i n e rocks reducing th e s iz e of the p a r t i c l e s near the
m o u n t a i n s w i t h r e s p e c t t o t h o s e f u r t h e r away.
therefore,
The i n c r e a s e i n s i z e woul d,
be p r i m a r i l y a f u n c t i o n o f t h e l e n g t h o f t i m e t h e s u r f a c e h as
22
be e n e x p o s e d t o w e a t h e r i n g r a t h e r t h a n t o c o n d i t i o n s a t t h e t i m e t h e s u r f a c e
was formedv
The d e c r e a s i n g v a l u e s f o r s p h e r i c i t y and r d u n d a e s s w i t h d i s t a n c e from
th e mountains a r e not e a s i l y e x p la in e d .
w er e d e p o s i t e d by an e a r l y g l a c i e r .
P e r h a p s t h e g r a v e l s on s u r f a c e I
A ncient moraine ten d s to be very sub­
dued ( s e e F i g u r e 13 and compare i t w i t h F i g u r e s 9 and 1 0 ) s
r e l a t i o n s h i p s would be e x p e c t e d t o be q u i t e e r r a t i c
I f t h e d e p o s it s a c t u a l l y a re moraine,
S tatistical
in d e p o s its o f m oraine.
the f o re g o in g arguments a r e p ro b a b ly
invalids
S u r f a c e I , wh ic h a p p e a r s t o be v e r y smooth when v ie w e d from any o f
th e lower s u r f a c e s ,
i s in r e a l i t y r a t h e r r o l l i n g .
I t i s l e s s smooth t h a n
any o f t h e O t h e r s u r f a c e s b u t s t i l l q u i t e l e v e l n e a r t h e c e n t r a l p a r t s o f
th e rem nants.
I
*
Headward e r o s i o n h as p r e c e d e d w e l l i n t o t h e e d g e s o f t h e s m a l l e r
r e m n a n t s o f s u r f a c e I and i n p l a c e s i t s
d le o f th e rem nant.
i n f l u e n c e e x t e n d s t o n e a r t h e m id­
'In t h e s e g e n t l e v a l l e y s ,
higher c o n cen tratio n s of
g r a v e l s a r e p r e s e n t a nd n e a r l y a lw a y s t h e g r a v e l s a r e s l i g h t l y l a r g e r ~ ~
than o u tsid e of th e v a lle y s .
U sually th e f l a t i n t e r i o r p a r t s o f s u rfa c e I
a r e c o v e r e d by s a g e and a t t h e s l o p e b r e a k s on a l l s i d e s , ' e v e r g r e e n t r e e s
grow i n a b u n d a n c e ;
E r o s i o n i s n o t e x t e n s i v e on t h e l a r g e r p a r , o f
I , h ow e ve r , and t h e o n l y p l a c e i t
a r e bounde d by s t r e a m s .
surface
i s n o t i c e a b l e i s a l o n g t h e e d g e s which
The e d g e s bo unded by s u r f a c e I I show v e r y l i t t l e
1-s I t m ig h t be U s e f u l t o m e n t i o n t h e d a n g e r i n a t t e m p t i n g t o d e l i n e a t e a
s u r f a c e by v i e w i n g t h e p r o f i l e a t a d i s t a n c e . A l t h o u g h t h e p r o f i l e may
a p p e a r t o b e v e r y f l a t and e x t e n s i v e , i n r e a l i t y i t may be n o t h i n g more
t h a n a r i d g e o r , i n t h e p r e s e n t a r e a , o n l y a dike.-
23
w a s t a g e and i t a p p e a r s t h a t c o n d i t i o n s i n t h e s e a r e a s a r e n e a r l y , i d e n t i c a l
to t h o s e when s u r f a c e J I was f o r m e d .
However, e r o s i o n i s p r e c e d i n g a t a
m o d e r a t e p a c e e s p e c i a l l y a l o n g t h e s o u t h s l o p e o f s u r f a c e I where L i t t l e
Rock C r e e k f l o w s t o t h e s o u t h w e s t t h r o u g h s e c t i o n s 16,
N., R. 11 Ei
17, and 19 o f T„ 2
Her e s l u m p i n g i s p r o n o u n c e d and g r a v e l s a r e b e i n g u n d e r m i n e d
t o s u c h an e x t e n t t h a t i n some p l a c e s t h e e a r t h a r o u n d t r e e r o o t s y s te m s
h a s be e n r em o v e d .
N orthern s lo p e s a r e smoother than th e so u th e rn ,
a con­
sequence o f scarp s lo p e -d ip slo p e r e l a t i o n s h i p s in rocks with n o r th e r ly dip,
and i n most p l a c e s w e a t h e r i n g i s n o t p a r t i c u l a r l y n o t i c e a b l e on t h e s e
slopes.
Although q u a n t i t a t i v e d a ta a r e not a v a i l a b l e ,
i t seems l i k e l y t h a t
s u r f a c e I r e c e i v e s more p r e c i p i t a t i o n t h a n any o t h e r s u r f a c e by r e a s o n o f
its
e l e v a t i o n and p r o x i m i t y t o t h e m o u n t a i n s .
face II,
s u r f a c e I r e c e i v e s snow.
Indeed,
O f t e n when i t r a i n s on s u r ­
a d i f f e r e n c e o f o n ly a hundred
f e e t o f e le v a ti o n i s a very im portant f a c t o r in d eterm ining both th e
amount and form o f p r e c i p i t a t i o n .
S u rfa c e I i s .the o l d e s t s u r f a c e o f a p p r e c i a b l e e x te n t observed in
the area.
I t s o r i g i n a l e x t e n t was c l e a r l y much g r e a t e r t h a n i t i s a t t h e
p rese n t tim e.
Location o f remnants i n d i c a t e t h a t i t
now o c c u p i e d by t h e v a l l e y o f Hammond C r e e k ;
tain;
extended over th e a re a
i t pro b ab ly co v ered Elk fo u n ­
and i t may h a v e e x t e n d e d f u r t h e r e a s t t h a n F a l l s C r e e k .
mipimum l i m i t s i n d i c a t e d by f i e l d e v i d e n c e .
These a r e
I t seems p r o b a b l e t h a t t h e
s u r f a c e a c t u a l l y c o v e r e d f a r more a r e a t h a n t h e s e l i m i t s would i n d i c a t e and
although co n firm a to ry f i e l d evidence i s lac k in g ,
s e v e r a l r e m n a n t s on t h e
e a s t and s o u t h s i d e s o f t h e m o u n t a i n s a p p e a r t o b e e q u i v a l e n t t o s u r f a c e I .
(
I
24
A maximum l i m i t f o r t h e s o u t h w e s t e r n b o u n d a r y m ig h t be t h e a n c e s t r a l S h i e l d s
H ivere but i t
i s n o t known wh er e t h i s wa s.
I t may n o t hav e be e n i n i t s
present p o sitio n .
F i e l d e v i d e n c e d oe s n o t i n d i c a t e what t h e ag e o f s u r f a c e I i s .
It is
o l d e r t h a n t h e f i r s t o f t h e two r e c o g n i z e d g l a c i a l a d v a n c e s i n t h i s a r e a ,
a nd , o f c o u r s e ,
o ld e r than su rfa c e I I .
I t may be y o u n g e r t h a n t h e T e r t i a r y
d e p o s i t s o f t h e Bozeman a r e a ( s e e p a g e 8 5 ) .
Surface I I
A v e r y r e g u l a r and e x t e n s i v e s u r f a c e i s d e v e l o p e d j u s t
s o u t h o f Hock
and L i t t l e Rock C r e e k s a s w e l l a s a b o u t a m i l e s o u t h o f Elk Mou nta in ( s e e
F i g u r e . I),.
In a d d i t i o n , t h e r e a r e s e v e r a l s m a l l e r r e m n a n t s w h ic h w er e on c e
c o e x t e n s i v e w i t h t h e s u r f a c e . Chose H i l l , A n t e l o p e B u t t e and C h o k e - t o - D e a t h
B u tte b eing n o ta b le examples.
S u r f a c e I I h e a d s v e r y n e a r t h e m o u n ta in
f r o n t a t a s l i g h t l y l o w e r e l e v a t i o n t h a n s u r f a c e I and e x t e n d s n e a r l y t o
th e S h ie ld ’s River,
a d ista n c e of over t h ir te e n m iles.
In t h i s d i s t a n c e i t
s l o p e s from a h i g h o f 7200 f e e t down t o n e a r l y 5100 f e e t .
tains,
Near t h e moun­
t h e g r a d i e n t i s q u i t e s t e e p , n e a r l y 400 f e e t p e r m i l e ,
r a p i d l y f l a t t e n s o u t t o a b o u t 150 f e e t p e r m i l e ,
but th is
a g r a d i e n t t h a t i s main­
t a i n e d e x c e p t f o r m in o r v a r i a t i o n s t h r o u g h o u t t h e r e m a i n d e r o f t h e l e n g t h .
The t o t a l a r e a o f s u r f a c e I I as d e t e r m i n e d by p o l a r p l a n i m e t e r i s
v e ry n e a r l y 1 5 -square m ile s ,
th e area is contiguous;
bu tes very l i t t l e
a l l remnants i n c lu d e d .
The l a r g e s t p a r t o f
t h e a r e a o f t h e s m a l l e r r e m n a n ts a c t u a l l y c o n t r i ­
to the t o t a l .
The h i g h e s t r e a c h e s o f t h e s u r f a c e a r e c o v e r e d by m o r a i n e from two
25
F i g u r e 12.
View e a s t o v e r Rock C r e e k a t s u r f a c e I I (B)
and s u r f a c e I ( C ) . The a r e a c o v e r e d by t h e u p p e r row
o f t r e e s (A) i s m o r a i n e .
F i g u r e 13. Near t h e h e a d o f s u r f a c e I I i n s e c t i o n 15,
I . 2 N . , R. 11 E. Subdued m o r a i n e o f t h e e a r l i e s t
g l a c i a l a d v a n c e l y i n g on t h e s o u t h e a s t edge o f t h e s u r ­
face.
The l a r g e s t b o u l d e r i n t h e c e n t e r (A) i s f i v e
feet across.
26
F i g u r e 14. Remnants o f s u r f a c e I I (A) a b o u t f o u r m i l e s
n o r t h e a s t o f C h a d b o r n . T h e s e r e m n a n t s a r e c o v e r e d by
a thin gravel cap.
Foreground is th e poorly developed
s u rfa c e e a s t of F id d le Creek.
F i g u r e 15.
S u r f a c e I I (A) a b o u t two m i l e s n o r t h e a s t o f
C h a d b o n i . C r a z y M ou n ta i n s i n t h e d i s t a n c e on t h e r i g h t .
F i g u r e 16.
Photo t a k e n j u s t n o r t h o f Rock Cr e e k on s u r f a c e I I I (C) in s e c t i o n 29,
T„ 2 N., R. 10 E. l o o k i n g n o r t h e a s t .
S u r f a c e I I (A) i s se en on t h e l e f t j u s t above
s u r f a c e I I I , and abov e i t i s s u r f a c e I ( B ) , h e r e p a r t l y o b s c u r e d by t r e e s .
On t h e
r i g h t s i d e o f t h e p h o t o , abov e Rock C r e e k i s t h e s l o p e up t o s u r f a c e I .
In t h e
c e n t e r on t h e r i g h t s i d e o f t h e c r e e k , i s s u r f a c e I I .
The C r a z y Mou ntain s a r e in
t h e background.
28
F i g u r e 17.
T y p i c a l g r a v e l c a p on s u r ­
fac e I I . Contact of g rav e l with the
u n d e r l y i n g s e d i m e n t a r y r o c k s c a n be
s e e n i n lower l e f t .
g la c ia l advances.
The u p p e r p a r t s o f t h e s u r f a c e a r e a l s o c o v e r e d by g l a ­
c i a l ou t w a s h t o a d i s t a n c e o f a b o u t f o u r t o f i v e m i l e s from t h e m o r a i n e and
t h i s has had a t e n d e n c y t o o b s c u r e t h e o r i g i n a l g r a v e l c o v e r .
c o v e r , which does n o t show marked v a r i a t i o n
f o r t h e most p a r t ,
quite thin,
The g r a v e l
i n t h i c k n e s s on s u r f a c e I I ,
is,
r a n g i n g fro m a b o u t f i v e t o t w e n t y f e e t t h i c k
b u t w i t h no s y s t e m a t i c c h a n g e i n t h i c k n e s s .
S t r e a m s i n c i s e d i n s u r f a c e I I have n a r r o w v a l l e y s so t h a t t h e y do n o t
c o n t r i b u t e much t o t h e e r o s i o n o f t h e s u r f a c e .
Most o f t h e s e s t r e a m s have
s t e e p n o r t h v a l l e y w a l l s a s co mpared t o t h e s o u t h w a l l wh ic h i s more g e n t l e .
29
O b s e r v a t i o n s o f f h e g r a v e l c o v e r on s u r f a c e I I i n d i c a t e e x p e c t a b l e
r e l a t i o n s h i p s i n most i n s t a n c e s .
Appendix A o f t h i s t h e s i s c o n t a i n s s p e ­
c i f i c inform ation about th e g ra v e l cover in c e r t a i n d e sig n a ted l o c a l i t i e s
a nd t h e d i s c u s s i o n h e r e w i l l be c o n f i n e d t o g e n e r a l i z a t i o n s .
S p h e r i c i t y remains r e l a t i v e l y c o n s ta n t ,
w i t h d i s t a n c e from t h e m o u n t a i n f r o n t .
ten d in g to d ec re a se s l i g h t l y
However, t h e t e n d e n c y i s so s l i g h t
a s t o be s m a l l e r t h a n m i g h t be e x p e c t e d fro m t h e l i m i t s o f e r r o r o f t h e
observations.
S t a t i s t i c a l r e g r e s s i o n s - f o r s p h e r i c i t y we re r e g a r d e d a s
inconclusive.
Roundness,
fro m t h e m o u n t a i n s .
ho we ve r, d i d i n c r e a s e m a r k e d l y w i t h d i s t a n c e
This i s in c o n t r a s t w ith s u rfa c e I but perhaps i t
r e p r e s e n t s a more o r t h o d o x c o n d i t i o n .
The p e r c e n t a g e o f i g n e o u s f r a g m e n t s
d e c r e a s e d w i t h d i s t a n c e from t h e m o u n t a i n f r o n t and t h e a v e r a g e s i z e o f
p a r t i c l e s increased s li g h t ly ,
b u t a g a i n t h e d i f f e r e n c e was so s l i g h t as
t o be i n c o n c l u s i v e .
G enerally,
t h e i n f o r m a t i o n o b t a i n e d from t h e s t u d i e s o f t h e g r a v e l s
on s u r f a c e I I seems t o i n d i c a t e a t r a n s i t i o n from c o n d i t i o n s t h a t p r e v a i l e d
d u r i n g t h e f o r m a t i o n o f s u r f a c e I when c o m p a r a t i v e l y l e s s d i o r i t e was e x ­
p o s e d , and t h o s e t h a t - h a v e p r e d o m i n a t e d s i n c e t h e n .
t h e form ation o f s u rfa c e I I ,
abundant in t h e g r a v e l s .
I t appears t h a t during
t h e i g n e o u s m a t e r i a l s became i n c r e a s i n g l y
T h i s r e f l e c t s t h e c o n t i n u i n g r e m o v a l o f Fo yt
Union s e d i m e n t a r y r o c k s from t h e c e n t r a l m a s s i f u n t i l t h e y no l o n g e r i n ­
flu e n c e d c o n d itio n s to t h e e x te n t t h a t th ey did during th e form ation of
surface I.
S u r f a c e I I i s r e m a r k a b l y smooth and u n d i s t u r b e d by e r o s i o n e x c e p t
near the edges.
Those s t r e a m s wh ic h do c u t t h r o u g h t h e s u r f a c e hav e r a t h e r
30
n a r r o w and s h a l l o w v a l l e y s and w a s t a g e by s a p p i n g a l o n g t h e i r s l o p e s i s
neg lig ib le.
The m o st r a p i c | e r o s i o n i s i n t h e F a l l s C r e e k a r e a j u s t e a s t
and w e s t o f F a l l s C r e e k Canyo n.
In t h e Bock C r e e k a r e a ,
e ro sio n i s checked
by t h e p r e s e n c e o f s u r f a c e I I I b e tw e en t h e c r e e k and s u r f a c e I I ,
Where
s u r f a c e I I I i s a b s e n t , Rock C r e e k i s w o r k i n g i n t o t h e s u r f a c e b u t n o t t o a
great extent.
Much o f s u r f a c e I I i s c u l t i v a t e d and u s e d f o r wh e a t f a r m i n g .
Sm a ll
a r e a s n o r t h o f Bock C r e e k a r e i r r i g a t e d and t h e b a l a n c e i s p a s t u r e .
Several
g r a v e l p i t s on s u r f a c e I I p r o v i d e an a b u n d a n t s u p p l y o f g r a v e l f o r t h e l o c a l
roads.
The a g e o f t h i s
Miocene o r P l i o c e n e .
s u r f a c e h a s b e e n s t a t e d by A ld e n ( 1 9 32 ) t o b e e i t h e r
On t h e b a s i s o f e l e v a t i o n ,
h i s F l a x v i l l e g r a v e l complex,
n o r t h e a s t e r n M ont an a.
he i n c l u d e d s u r f a c e I I i n
f i r s t d e f i n e d by C o l l i e r a n d Thom (191 7) i n
For r e a s o n s t o be p r e s e n t e d l a t e r ,
I p r e f e r not to
t h i n k o f s u r f a c e I I a s b e i n g e q u i v a l e n t t o A l d e n "s F l a x v i l l e b u t r a t h e r a s
being o f e a r l y P le is to c e n e age.
The p o s s i b i l i t y a l s o e x i s t s t h a t t h e F l a x -
v i l l e i s a c t u a l l y o f e a r l y P l e i s t o c e n e a g e and h as b e e n m i s d a t e d by C o l l i e r
and Thom.
T h i s w i l l be d i s c u s s e d i n g r e a t e r d e t a i l l a t e r .
The y o u n g e r
s u r f a c e s ca n be d a t e d w i t h more a c c u r a c y w i t h r e s p e c t t o t h e two p e r i o d s
of glacial activ ity ,
but s t i l l not w ith s a t i s f a c t o r y p r e c is io n r e l a t i v e to
surface I I.
As shown by t h e d e p t h o f t h e g r a v e l c o v e r as w e l l a s by t h e s i z e and
im brication,
it
a p p e a r s most l i k e l y t h a t s u r f a c e I I ,
a s w e l l as s u r f a c e I ,
was fo rm ed by l a t e r a l l y c u t t i n g s t r e a m s o r i g i n a t i n g i n t h e n o r t h e a s t .
a s Rock C r e e k i s c u r r e n t l y i n t h e p r o c e s s o f c u t t i n g a s u r f a c e ,
so was
Just
31
s u r f a c e I I c a r v e d by g r a d i n g s t r e a m s which moved l a t e r a l l y b a c k and f o r t h .
P e r h a p s n e a r e r t h e m o un ta in s *
s h e e t w a s h h a s be e n more e f f e c t i v e ,
especially
n e a r t h e a n g u l a r j u n c t i o n s o f t h e s u r f a c e w ith th e mountain f r o n t *
ab ov e r e a s o n i n g p o s t u l a t e s s e v e r a l s t a g e s f o r a s u r f a c e ,
narrow v a ll e y ,
le a d in g t o a wide f l o o d p l a i n ,
f i n a l l y t o t h e more e x t e n s i v e p e d i m e n t s .
The
beginning with a
and r o c k - c u t - t e r r a c e ,
and
This sequence i s s i m i l a r to
J o h n s o n ' s (193 2) t h e o r y o f p e d i m e n t s form ed by l a t e r a l l y p l a c a t i n g s t r e a m s .
Where one s t a g e e nd s and a n o t h e r b e g i n s i s p u r e l y a r b i t r a r y and n o t s o , im­
p o r t a n t a s an u n d e r s t a n d i n g o f t h e mechanism which c u t s t h e s u r f a c e s .
An e r r o r i n t h e U n i t e d S t a t e s G e o l o g i c a l Su rv ey G e o l o g i c map o f
Montana,
1955,
s h o u l d be c o r r e c t e d .
ponding to t h e p r e s e n t s u rf a c e I I i s
U n d ifferen tiated ,"
The a r e a o f "Ts" a p p a r e n t l y c o r r e s ­
l i s t e d as " T e r t i a r y Sedim entary Rocks-
This g iv e s the im pression of a s e dim entary sequence o f
some m a g n i t u d e a n d d e p t h , b u t i n r e a l i t y ;
s i s t of only a veneer o f g ra v e l.
th e s e " T e rtia r y sedim ents" con­
The a r e a s h o u l d be i n c l u d e d i n t h e F o r t
Union f o r m a t i o n , which u n d e r l i e s t h e s e g r a v e l s e v e r y w h e r e .
I f one i n s i s t s
on i n c l u d i n g t h i s thin l a y e r o f g r a v e l i n a " T e r t i a r y s e d i m e n t a r y s e q u e n c e " ,
then i t
is
i m p e r a t i v e t h a t t h e e q u a l l y t h i n g r a v e l v e n e e r s wh ic h c o v e r t h e
other surfaces,
an a r e a more t h a n t w i c e t h a t shown on t h e map, be i n c l u d e d
in t h e sequence t o o .
The a r e a o f "Ts" shown on t h e s t a t e map i s a l s o i n ­
c o r r e c t l y l o c a t e d b e c a u s e much o f t h e a r e a d e s i g n a t e d "T s " i s n o t even
c o v e r e d by g r a v e l so i t i s d i f f i c u l t t o s e e what t h e a u t h o r s o f t h e map
had i n m ind .
32
Surface I I I
S u r f a c e I I I i s w i d e l y e x p o s e d i n t h e a r e a s s o u t h o f Rock C r e e k and
n o r t h o f Cot to nw o od C r e e k ( s e e F i g u r e 1)„
c a lly separate areas,
comparable e l e v a t i o n s „
I t c o n s i s t s o f two g e o g r a p h i ­
no n e a r e r t h a n two m i l e s a p a r t w h i c h ,
however, hav e
Sm a ll r e m n a n t s o c c u r d i r e c t l y n o r t h o f Rock C r e e k
and n e a r t h e S h i e l d s R i v e r s e v e r a l s m a l l r e m n a n t s ha v e b e e n s e p a r a t e d from
t h e main body o f t h e s u r f a c e ,
t h o s e i n s e c t i o n s 3 and 34 o f T„ 2 N. and
T, 3 N„, R„ 9 E„ b e i n g t h e most n o t a b l e e x a m p l e s .
Surface H I c o n s is ts of
more t h a n 23 s q u a r e m i l e s o f e x c e e d i n g l y f l a t W h e at la n d on whi ch s l o p e s
a r e n e a r l y i m p e r c e p t i b l e e x c e p t s o u t h o f I b e x M o u n ta i n ,
IGO and 150 f e e t p e r m i l e ,
S l o p e s v a r y b e tw e en
steep er in the higher e le v a tio n s .
T he.northern
p a r t o f t h e s u r f a c e i s d e v e l o p e d b e tw e en t h e e l e v a t i o n s o f 5 0 0 0 . f e e t and.
6300 f e e t and t h e s o u t h e r n p a r t b e tw e e n 4800 f e e t and 5900 f e e t .
D i s s e c t i o n o f t h e s o u t h e r n p a r t o f t h e s u r f a c e i s most p r o n o u n c e d . ..
a l o n g . R o c k C r e e k a l t h o u g h s l o p e s h e r e a r e g e n t l e and t h e c a n y o n . , . c o n d i t i o n s ,
, p r e s e n t u p s t r e a m ha ve n o t d e v e l o p e d .
S e v e ra l small stream s a re eroding...
.
he a dw a rd i n t o t h e s o u t h e r n p a r t o f t h e s u r f a c e from t h e S h i e l d s R i v e r b u t
t h e l i m i t e d s i z e a n d i n t e r m i t t e n t c h a r a c t e r o f t h e s e s t r e a m s p r e v e n t s them
from moving s u b s t a n t i a l amounts o f m a t e r i a l .
The n o r t h e r n p a r t , o f . , t h e . ..
..
s u r f a c e i s b e i n g r a p i d l y e r o d e d by he ad wa rd s a p p i n g o f t r i b u t a r i e s o f f t h e
Shields R iver.
T h i s i s d ue i n p a r t t o t h e r e l a t i v e l y t h i n g r a v e l c o v e r ,
I n d i a n and L i t t l e
I n d i a n C r e e k s hav e c u t b a c k s e v e r a l m i l e s i n t o t h e s u r ­
f a c e and a l t h o u g h t h e y a r e s m a l l ,
t h e i r v a l l e y s a r e deep and slump and c r e e p
along t h e i r s id e s i s q u i t e pronounced.
Along t h e south s i d e o f Horse Creek
v a l l e y i n s e c t i o n s 28, 29, and 30, T. 3 N„, R, 10 E. a r e some m o d e r a t e l y
33
F i g u r e 18.
View l o o k i n g n o r t h e a s t o v e r t h e S h i e l d s R i v e r n e a r C h a d b o r n .
The h i g h e s t s u r f a c e (C) i s I I and b e lo w i t i s I I I ( B ) . Below s u r f a c e I I I
i s t h e v a g u e l y d i s c e r n i b l e t e r r a c e (A) abov e t h e S h i e l d s f l o o d p l a i n ( D ) .
Headward e r o s i o n i n t o s u r f a c e I I I h as n o t accomplished much d i s s e c t i o n on
the te r r a c e .
F i g u r e 19. View t h r e e m i l e s n o r t h o f Chad bo rn on t h e
y o u n g e r o f t h e two S h i e l d s R i v e r t e r r a c e s ( C ) ; l o o k i n g
s o u th e a s t to s u rf a c e I I I (A).
Notice the c h a r a c te r of
t h e s l o p e s e x t e n d i n g from s u r f a c e I I I t o t h e t e r r a c e ( B ) .
f i g u r e 20.
Phot o t a k e n d i r e c t Iy s o u t h o f Chadborn l o o k i n g n o r t h e a s t a c r o s s t h e S h i e l d s
R iver Valley.
The h i g h s u r f a c e on t h e l e f t (A) i s s u r f a c e I I ( s e e F i g u r e 14 f o r a c l o s e up o f t h i s same a r e a ) .
At C i s t h e m a t u r e t o p o g r a p h y s o u t h o f s u r f a c e I I .
The C r a z y
M o un ta in s a r e i n t h e f a r d i s t a n c e a t B.
35
l a r g e l a n d s l i d e s which h a v e n o t y e t bee n e r o d e d away.
th is erosion,
As a - c o n s e q u e n c e o f
t h e n o r t h e r n p a r t o f s u r f a c e I I I h as s e v e r a l l o n g e x t e n s i o n s
wh ic h h a v e b e e n n e a r l y c u t o f f from t h e main body o f t h e s u r f a c e .
S l o p e s from s u r f a c e I I t o s u r f a c e I I I a r e g u l l i e d and c a r v e d o u t
c o n s i d e r a b l y , and y e t . t h e r e seems t o be no p e r p e t u a t i o n o f t h e s e g u l l i e s
i n t o t h e lower s u r f a c e .
T h i s would seem t o i n d i c a t e t h a t s i n c e t h e s t a ­
b iliz a tio n of surface I I I ,
t h e g u l l y i n g h a s been n e g l i g i b l e .
These s lo p e s
a r e w e l l r o u n d e d and t h e y do n o t a p p e a r t o b e c h a n g i n g a t t h e p r e s e n t t i m e .
The r e g u l a r c o n t i n u a t i o n o f t h e s l o p e l i n e o v e r a d i s t a n c e o f a b o u t f i v e
m i l e s s u g g e s t s t h a t i t may r e p r e s e n t a ba n k a l o n g which a s t r e a m o r r i v e r
which f a s h i o n e d t h e s u r f a c e f l o w e d .
The g r a v e l c o v e r on t h e n o r t h e r n p a r t o f t h e s u r f a c e i s t h i n ;
p laces ten f e e t or le s s ,
i n most
w i t h no s y s t e m a t i c t e n d e n c y t o w a r d a t h i c k e n i n g
o r t h i n n i n g i n any d i r e c t i o n .
The i m b r i c a t i o n i n v a r i a b l y i n d i c a t e s t h a t
t h e g r a v e l s wer e d e p o s i t e d i n s t r e a m s moving from t h e n o r t h e a s t w h e r e a s
on t h e s o u t h e r n p a r t o f t h e s u r f a c e ,
s i t i o n from t h e n o r t h .
i m b r i c a t i o n some time s s u g g e s t s d e p o ­
Gravel fragm ents a re g e n e r a lly sm all in s i z e a l ­
t h o u g h i n some e x p o s u r e s b o u l d e r s up t o a f o o t i n d i a m e t e r a r e p r e s e n t .
The a v e r a g e maximum d i a m e t e r o f t h e s e g r a v e l s t e n d s t o d e c r e a s e w i t h d i s ­
t a n c e from t h e m o u n t a i n s ( s e e F i g u r e 2 6 ) .
C r y s t a l l i n e rocks c o n s t i t u t e
s m a l l e r p e r c e n t a g e s o f t h e g r a v e l a s o n e moves away from t h e m o u nt a in
f r o n t , w h e r e a s b o t h s p h e r i c i t y and r o u n d n e s s i n c r e a s e c o r r e s p o n d i n g l y .
These r e l a t i o n s h i p s a r e normal in t h e sense t h a t s i m i l a r r e l a t i o n s h i p s
ha ve bee n o b s e r v e d i n p r e v i o u s s t u d i e s i n o t h e r a r e a s ( P l u m l e y ,
Montagne,
1951).
1948;
They seem t o im p ly c o n d i t i o n s s i m i l a r t o t h e p r e s e n t
36
t i m e w i t h c o m p a r a b l e amo unt s o f F o r t Union s e d i m e n t a r y r o c k s e x p o s e d r e l a ­
t iv e to c r y s t a l l i n e ro c k s .
D ip s o f t h e F o r t Union a l o n g t h e s i d e s o f t h e s u r f a c e a r e low; m o s t l y
l e s s t h a n IO0 n o r t h .
Most o f s u r f a c e I I I i s c u l t i v a t e d a s wh e a t l a n d and
p a r t s o f i t a r e i r r i g a t e d w i t h w a t e r fro m Cot to nw oo d C r e e k and Rock C r e e k .
S o u t h o f I b e x M o u n ta i n , t h e u p p e r p a r t s o f t h e s u r f a c e g r a d e i n t o t h e
o l d e s t m o r a i n e and e v i d e n t l y much o f t h e u p p e r a r e a o f t h e s u r f a c e i s c o v ­
e r e d by r e l a t e d g l a c i a l o u t w a s h a l t h o u g h i t
i s i m p o s s i b l e t o d e t e r m i n e how
much o f t h e g r a v e l ca n be d i r e c t l y a t t r i b u t e d t o t h i s c a u s e .
Deposits
from t h e most r e c e n t g l a c i a t i o n a r e n o t p r e s e n t on s u r f a c e I I I .
Alde n ( 1 932 ) mapped t h e n o r t h e r n p a r t o f s u r f a c e I I I as a "Remnant o f
a s e c o n d o r m e d i a l b e nc h o f s t r e a m t e r r a c e s and a l l u v i a l f a n s , ; "
n o t map t h e s o u t h e r n p a r t o f t h e s u r f a c e .
P le is to c e n e pre-Iowan or I l l i n o i s a n
t i o n i s as f o l l o w s ;
He d i d
He g i v e s t h e a g e a s " E a r l y
(?) i n t e r g l a c i a l s t a g e . "
His d e s c r i p ­
"Cut t e r r a c e s and p l a n a t e d s u r f a c e s m o s t l y c o v e r e d by
d e p o s i t s o f s m o o t h l y worn n o n g l a c i a l g r a v e l d e r i v e d from t h e m o u n t a i n s and
i n p l a c e s c e m e n te d t o c o n g l o m e r a t e .
I n c l u d e s some g r a v e l p r o b a b l y d e r i v e d
from o l d e r and h i g h e r t e r r a c e s . "
A l d e n ' s s t a t e m e n t a s g i v e n abov e may be v a l i d ,
b u t he s h o u l d have
i n c l u d e d t h e s o u t h e r n p a r t o f t h e s u r f a c e on h i s map b e c a u s e i t f i t s t h e
d e s c rip tio n equally w e ll.
There i s ,
ho wev er ,
The e a r l y P l e i s t o c e n e ag e i s n o t u n r e a s o n a b l e .
some d o u b t a s t o w h e t h e r t h e s u r f a c e s h o u l d be c l a s s i ­
f ie d as g l a c i a l or i n t e r g l a c i a l .
The p r e s e n c e o f t h e g l a c i a l l y m o d i f i e d
g r a v e l s on t h e u p p e r r e a c h e s o f t h e s u r f a c e m i g h t i n d i c a t e t h a t i t was
formed by s t r e a m s i s s u i n g frpm an a d v a n c i n g ,
retreating,
or statio n ary
37
glacier.
The s u r f a c e was p r o b a b l y c u t by l a t e r a l l y m i g r a t i n g s t r e a m s from
t h e n o r t h and n o r t h e a s t r e g a r d l e s s o f what t h e s o u r c e o f t h o s e s t r e a m s may
have been.
S u r f a c e I I I was o n c e much more e x t e n s i v e a l t h o u g h t h e l i m i t s o f i t
a r e n o t d e f i n i t e l y known.
I t c o v e r e d much o f t h e a r e a b e tw e e n Bock and
Co tt o n w o o d C r e e k s , a l l t h e a r e a now o c c u p i e d by I n d i a n and L i t t l e I n d i a n
C r e e k v a l l e y s a s w e l l a s t h e a r e a s now o c c u p i e d by a l l
wh ic h a r e now e r o d i n g i t .
the l e s s e r streams
I t v e r y l i k e l y e x t e n d e d t o t h e n o r t h o v e r what
i s now H o r s e C r e e k v a l l e y and even be yond t h e a r e a c o v e r e d by t h e p r e s e n t
s t u d y a s e v i d e n c e d by t h e b r o a d e r o s i o n s u r f a c e s n o r t h o f t h e mapped a r e a .
were
I ha v e c o n c l u d e d t h a t t h e n o r t h e r n
and s o u t h e r n p a r t s o f s u r f a c e I I I
o n c e c o e x t e n s i v e and f o rm e d d u r i n g
t h e same c y c l e o f e r o s i o n .
Remnants
i n t h e two a r e a s a r e n o t n e a r e r t h a n two m i l e s a p a r t , b u t even s o , e l e v a ­
tio n s are f a i r l y accordant.
S t a t i s t i c a l s t u d i e s do n o t i n d i c a t e any s i g ­
n i f i c a n t d i f f e r e n c e s in th e g ra v e l co v ers except, perhaps,
t io n s in s iz e s ,
for the v a ria ­
a c o n d i t i o n t h a t m ig h t b e e x p l a i n e d by t h e p r e s e n c e o f
moraine in t h e n o rth e rn a r e a .
The c u r v e s f o r s p h e r i c i t y and r o u n d n e s s a r e
n e a r l y p a r a l l e l f o r t h e two a r e a s ( s e e F i g u r e s 2 3 and 2 5 ) .
Finally,
the
g e o g r a p h i c p o s i t i o n s o f t h e two a r e a s w i t h r e s p e c t t o one a n o t h e r p l u s t h e
f a c t t h a t no h i g h o b s t a c l e s l i e b e tw e en them, a r e b o t h f a v o r a b l e i n d i c a ­
tio n s fo r contem poraniety.
S u r f a c e IV
Along much o f t h e c o u r s e o f Cot to n wo o d C r e e k i s a n a r r o w s u r f a c e w i t h
a t o t a l area, o f a b o u t
s ix square m ile s.
I t e x t e n d s from j u s t
south of
38
I b e x M ou nt a in w h e r e i t
has an e l e v a t i o n o f a b o u t 6200 f e e t down t o C l y d e
P a r k wh er e t h e e l e v a t i o n i s 4900 f e e t , .
At C l y d e P a r k i t m er g e s w i t h a
S h i e l d s R i v e r t e r r a c e w hi ch l i e s a b o u t 50 f e e t abov e t h e p r e s e n t f l o o d p l a i n
at th is point.
The s u r f a c e i s q u i t e l e v e l and w e l l d e f i n e d i n most p l a c e s ,
e s p e c i a l l y where i t
i s bou nde d by s u r f a c e I I I .
e a s t o f Clyde Park,
i t m er ge s w i t h t h e m a t u r e t o p o g r a p h y b e tw e en Squ aw 's
T i t and Chose H i l l .
I t i s c e r t a i n l y e x t e n s i v e enough t o be d e s i g n a t e d
"surface",
However,
in the area n o rth ­
b n t s t i l l n a r r o w eno ugh t o s u g g e s t t h a t i t was f or m e d a s a
stream t e r r a c e .
G r a v e l s on s u r f a c e IV show g r e a t v a r i a t i o n i n s i z e from n o r t h e a s t t o
southw est (se e F ig u re 2 6 ),
Both s p h e r i c i t y and r o u n d n e s s i n c r e a s e more w i t h
t r a n s p o r t d i s t a n c e t h a n on any o t h e r s u r f a c e ,
l i n e g r a v e ls d e c re a se s m arkedly.
and t h e p e r c e n t a g e o f c r y s t a l ­
Th e g r a v e l s on t h e h i g h e s t r e a c h e s o f t h e
s u r f a c e h a v e b e e n d e r i v e d from t h e m o r a i n e w hi ch c o v e r s t h e a r e a h e r e .
The
e n t i r e a r e a j u s t n o r t h o f E l k Mou nta in i s c o v e r e d by i n o r d i n a t e l y l a r g e
g r a v e l s due t o t h i s
source.
Most g r a v e l s seem t o have be e n c a r r i e d from
the n o rth east or e a st-n o rth e a s t,
that is,
s e n t d i r e c t i o n o f C ot to n w o od C r e e k .
e s s e n t i a l l y p a r a l l e l to th e p r e ­
The t h i c k n e s s o f "the g r a v e l cover,
seems t o d i m i n i s h t o w a r d t h e s o u t h w e s t , p e r h a p s i n d i c a t i n g t h e p r e s e n c e o f
g l a c i a l o u t w a s h on t h e h i g h e r r e a c h e s o f t h e s u r f a c e .
G enerally,
the g r a ­
v e l c o v e r on s u r f a c e IV i s t h i c k e r t h a n on t h e o t h e r s u r f a c e s and r a n g e s
up t o 30 f e e t i n t h e n o r t h e a s t .
Co tt o n w o o d C r e e k , a s a l r e a d y m e n t i o n e d ,
fo llo w s a c o u rs e keeping i t
e i t h e r a d j a c e n t t o o r w i t h i n s u r f a c e IV t h r o u g h o u t much o f i t s
length.
i s e n t r e n c h e d , b e lo w t h e s u r f a c e a b o u t 100 f e e t a l o n g a l m o s t a l l o f t h i s
It
39
distance.
The c a n y o n - l i k e v a l l e y t h r o u g h which Cot to nw oo d C r e e k f l o w s i s
w i d e n i n g t o some d e g r e e a s e v i d e n c e d by t h e s e v e r a l r e c e n t l a n d s l i d e s ,
p e c i a l l y e a s t o f C ot to n w o o d Bench,
es­
Except f o r t h i s , e ro s io n i s n e g l i g i b l e
on s u r f a c e IV a s v e r y fe w s t r e a m s a r e e r o d i n g t h e i r way he a d wa rd i n t o t h e
surface.
The s l o p e s from s u r f a c e I I I t o IV a r e i n t r i c a t e l y d i s s e c t e d and
rounded but q u i t e s t a b l e .
The d i s s e c t i o n o f t h e s e s l o p e s e v i d e n t l y was
a c c o m p l i s h e d When Cot to nw o od C r e e k f lo w e d a d j a c e n t t o s u r f a c e I I I on s u r ­
f a c e IV.
A f t e r i t moved away from t h e s e s l o p e s ,
s ta b i li ty prevailed.
S u r f a c e IV c a n be d a t e d a s y o u n g e r t h a n t h e o l d e r o f t h e two known
g l a c i a l s t a g e s and e i t h e r o l d e r o r c o n t e m p o r a n e o u s w i t h t h e y o u n g e r g l a c i a l
stage.
T h i s i n f o r m a t i o n i s s u f f i c i e n t t o a s s i g n an ag e o f l a t e P l e i s t o c e n e
to the su rfa c e.
Furtherm ore,
i t i s s u f f i c i e n t evidence to s t a t e t h a t the
l o w e r ca nyon o f C ot to n w o od C r e e k was c u t s i n c e l a t e P l e i s t o c e n e .
The s u r f a c e j u s t s o u t h o f Sq ua w 's T i t , w h ic h i s i n t e r m e d i a t e betw een
surfaces
I I I and IV, i s s e p a r a t e d from s u r f a c e IV by a sm ooth,
ment a b o u t 2 0 - 3 0 f e e t h i g h .
even e s c a r p ­
T h i s s u r f a c e must r e p r e s e n t an i n t e r m e d i a t e
s t a g e be tw e e n s u r f a c e s I I I and IV; p e r h a p s Cotto nwo od C r e e k f lo w e d e a s t o f
S q u a w 's T i t a t one t i m e .
F inally,
t h e s m a l l t e r r a c e - l i k e a r e a d i r e c t l y b e lo w s u r f a c e IV j u s t
n o r t h e a s t o f C l y d e P a r k , must r e p r e s e n t a f i n a l s t a g e whi ch was c u t a f t e r
Cot to nw o od C r e e k had a l r e a d y l e f t t h e r e m a i n d e r o f s u r f a c e IV.
although i t
i s not e x te n s iv e ,
S u r f a c e IV,
is im portant in t h a t i t i l l u s t r a t e s q u ite
w e l l a s u r f a c e t h a t h as o b v i o u s l y been c u t by a l a t e r a l l y p l a n a t i n g stream..
Surface J ------ (
Surface H — —
Surface m i -----horft)
S u r f a c e HT -----soo+K
Surface IST
• ® —-------
F i g u r e 21 . C o m p o s it e p r o f i l e s o f s u r f a c e s s o u t h w e s t o f t h e C r a z y M ou nta in s a s s e m b le d a c c o r d i n g t o
estim ated r e l a t i v e p o s i t i o n s .
I
41
S hields River Terraces
An e x t e n s i v e and v e r y f l a t t e r r a c e l i e s a l o n g t h e e a s t e r n s i d e of
t h e S h i e l d s R i v e r from a b o u t a m i l e n o r t h o f C l y d e P a r k t o a s f a r s o u t h as
Ch a db or n w h e r e i t d e t e r i o r a t e s and a p p e a r s t o be c u t by t h e s l o p e s from
surface II.
In t h e s o u t h e r n p a r t s ,
t h i s t e r r a c e l i e s a b o u t 80 f e e t abov e
t h e p r e s e n t f l o o d p l a in but t h i s v e r t i c a l s e p a r a ti o n d im in ish e s northw ard to
l e s s t h a n 20 f e e t ,
and t h e t e r r a c e f i n a l l y l o s e s i t s
tio n s h i p suggests broad re g io n a l t i l t i n g
id en tity .
Such a r e l a ­
in l a t e P le is t o c e n e tim e,
s i d e b e in g lowered r e l a t i v e to t h e south s i d e .
the north
A n o t h e r p o s s i b i l i t y m ig h t
be a l o w e r i n g b a s e l e v e l i n t h e s o u t h e r n p a r t o f t h e a r e a .
Such a c o n d i t i o n
would h e l p t o e x p l a i n t h e f a c t t h a t t h e s o u t h e r n p a r t o f t h e mapped a r e a
h a s bee n more d e e p l y e r o d e d t h a n t h e n o r t h .
R i v e r m ig h t a c c o u n t f o r t h i s e r o s i o n .
Clyde Park i n d i c a t i n g i t
The p r o x i m i t y o f t h e Y e l l o w s t o n e
The t e r r a c e m erg es w i t h s u r f a c e IV a t
i s t h e same a g e a s t h a t s u r f a c e .
G r a v e l s on t h i s t e r r a c e a r e i m b r i c a t e from t h e n o r t h w e s t and a l t h o u g h
t h e y a r e m o s t l y s i m i l a r t o t h o s e e x p o s e d on t h e o t h e r s u r f a c e s ,
a few c o b ­
b l e s o f q u a r t z i t e o f t h e B e l t s e r i e s a r e p r e s e n t a s w e l l a s some c o b b l e s o f
Meagher l i m e s t o n e .
No c o m p a r a b l e t e r r a c e i s p r e s e n t on t h e w e s t s i d e o f t h e S h i e l d s
R i v e r w he r e t h e t o p o g r a p h y i s t h o r o u g h l y d i s s e c t e d and h i l l y .
No s u r f a c e s
c o m p a r a b l e t o t h o s e b e tw e en t h e S h i e l d s a n d t h e C r a z y M o u n ta i n s a r e p r e s e n t
to th e west.
The s l o p e s from s u r f a c e I I I t o t h e S h i e l d s R i v e r t e r r a c e a r e s t e e p
b u t n o t a c t i v e and a l t h o u g h s e v e r a l s m a l l s t r e a m s f l o w i n g on t h e t e r r a c e do
he a d b a c k i n t o t h e o l d e r ,
higher surfaces,
th ey accomplish only s l i g h t '
am ounts o f e r o s i o n a f t e r t h e y p a s s on t o t h e t e r r a c e s ,
I
42
Two m i l e s s o u t h e a s t o f Chadborn on t h e e a s t s i d e o f t h e S h i e l d s R i v e r
a r e some s m a l l t e r r a c e r e m n a n t s a t an e l e v a t i o n o f a b o u t 250 f e e t dbove t h e
present floodplain.
spicuous.
Because they a r e i s o l a t e d ,
these h i l l s are q u ite con­
They a p p e a r t o h a v e been c o e x t e n s i v e w i t h t h e p o o r l y d e v e l o p e d
surface to the east,
and a l t h o u g h t h i s may be s o , t h e p r e s e n c e o f g r a v e l s
from t h e B e l t , ' Meagher and P h o s p h o r i a f o r m a t i o n s i n d i c a t e t h a t e i t h e r t h e
S h i e l d s R i v e r o r t h e Y e l l o w s t o n e R i v e r must h a v e flo w ed on them a t one
tim e.
T he s e g r a v e l s m i n g l e w i t h t h e t y p i c a l C r a z y M o u n ta i n s s u i t e ,
and t h e r a l i t i c
dioritic
g r a v e l s w i t h a d m i x t u r e s o f F o r t Union c o b b l e s .
The r e m o v a l o f 250 f e e t o f s e d i m e n t s must have t a k e n a lo n g t i m e .
The e l e v a t i o n o f t h e h i g h e s t o f t h e s e r e m n a n t s i s o v e r 4800 f e e t s u g g e s t i n g
t h a t t h e a n c e s t r a l S h i e l d s R i v e r ( o r t h e Y e l l o w s t o n e R i v e r ) may hav e been
f l o w i n g on a l e v e l e q u i v a l e n t t o s u r f a c e I I I t o t h e n o r t h .
r e m n a n t s may b e t h e same age a s s u r f a c e I I I .
Therefore* th e
On t h e o t h e r h a n d ,
g r a d i e n t o f t h e S h i e l d s R i v e r was g r e a t e r a t t h e t i m e t h a n i t
i f t h e t i l t i n g p o s t u l a t e d on p a g e 41 a c t u a l l y h a s t a k e n p l a c e ,
i f the
i s now, o r
th e remnants
may b e t h e same a g e a s s u r f a c e I I .
Alluvium
A l l o b s e r v e d r e c e n t a l l u v i a l d e p o s i t s a r e shown on t h e map ( F i g u r e I ) .
G enerally,
o n l y t h e two l a r g e s t s t r e a m s , Cotton woo d and Rock C r e e k s ,
a d d itio n to th e S hields R iver,
hav e m ap p a b le amounts o f d e p o s i t s .
in
Thes e
d e p o s i t s c o n s i s t p r i m a r i l y o f l a r g e c o b b l e s from t h e C r a z y M o u nt a in s as
w e l l as some r e w o r k e d g r a v e l s from t h e s u r r o u n d i n g s u r f a c e s .
Very l i t t l e
m a t e r i a l from t h e u n d e r l y i n g s e d i m e n t a r y r o c k i s i n c o r p o r a t e d i n t o t h e
43
alluvium because i t
stream s.
i s g e n e r a l l y removed a s f a s t a s i t i s ad d e d t o t h e
S c a t t e r e d b u t l i m i t e d amounts o f c o l l u v i u m a r e p r e s e p t on some
o f t h e s t e e p e r s l o p e s b u t no a t t e m p t was made t o map t h e s e d e p o s i t s .
RESULTS OF THE STATISTICAL STUDIES
F o r t y - t w o s e p a r a t e s t u d i e s o f t h e g r a v e l s were u n d e r t a k e n a t c a r e ­
f u l l y s e l e c t e d l o c a t i o n s on e a c h s u r f a c e ,
( S e e A p pe n di x A .)
Each s t u d y
i n c l u d e d c a r e f u l m e a s u r e m e n ts o f t h e s p h e r i c i t y and maximum d i a m e t e r o f f i f t y
s p e c i m e n s a s w e l l as o b s e r v a t i o n s o f t h e r o u n d n e s s , c o m p o s i t i o n ,
of th e s e specimens.
and b r e a k a g e
L o c a t i o n s f o r e a c h s t u d y were c a r e f u l l y s e l e c t e d i n
s uc h a way a s t o d e r i v e maximum i n f o r m a t i o n .
from t h e s e l e c t e d l o c a t i o n ^
u s u a l l y by w a l k i n g
Sp ecimens w e r e c h o s e n a t random
in
p i c k i n g a c e r t a i n number o f r o c k s e v e r y fe w p a c e s .
a random l i n e and b l i n d l y
E v e r y e f f o r t was made t o
e l i m i n a t e b i a s from t h e s a m p l i n g p r o c e d u r e .
Only s p e c i m e n s o f one i n c h o r more i n d i a m e t e r were s e l e c t e d s i n c e
s m a l l e r s i z e d s a m p l e s would r e q u i r e g r e a t l y m o d i f i e d s a m p l i n g t e c h n i q u e s .
In s e v e r a l a r e a s t h e s i z e o f t h e s p e c i m e n s was su ch t h a t r e m o v a l o f t h e
samp le t o t h e camp was deemed i n e x p e d i e n t and m ea s u r em e n ts w e r e made d i r ­
e c t l y in th e f i e l d .
O b s e r v a t i o n s r e g a r d i n g t h e im m e d i a te a r e a were r e ­
c o rd ed f o r each sample l o c a l i t y .
A l t h o u g h s e v e r a l met ho ds f o r p r e s e n t i n g t h e i n f o r m a t i o n o b t a i n e d and
i m p l i e d fr om t h e s t u d i e s wer e c o n s i d e r e d ,
d e c i d e d upon s i n c e i t
a g r a p h i c a l a p p r o a c h was f i n a l l y
i s most r e a d i l y and v i v i d l y u n d e r s t o o d .
E xplanations
accompany e a c h g r a p h .
W a d e l l (193 2) was t h e f i r s t t o show t h a t t h e commonly u s e d t e r m s
44
" s h a p e " and " r o u n d n e s s " wer e n o t synonymous, b u t r e a l l y
m e tric a lly d is tin c t concepts.
i n c l u d e d two g e o ­
Shape o f a r o c k i s i t s fo rm ,
pendent o f w hether t h e edges o r c o rn e r s a r e sharp or round.
e n tir e ly inde­
W hile t h e
s h a p e i s most a c c u r a t e l y e x p r e s s e d a s t h e r a t i o o f s u r f a c e a r e a t o volume,
i t c a n be s a t i s f a c t o r i l y d e t e r m i n e d by m e a s u r i n g t h e t h r e e m a j o r a x e s o f
the rock.
R ou nd ne ss i s a m e a s u r e o f t h e e u f v a t u r e o f t h e c o r n e r s and e d g e s
ex p ressed as a r a t i o
to
t h e a v e r a g e c u r v a t u r e o f t h e p a r t i c l e a s a who le,
independent o f i t s form.
"Method o f d e t e r m i n i n g s p h e r i c i t y A l l r o c k s c a n be c o n s i d e r e d t o p o s s e s s t h r e e m a j o r a x e s a t r i g h t
i
Angles to each o t h e r ;
the f i r s t
long ( a ) ,
interm ediate (b),
two o r s e c o n d two o f t h e s e may b e e q u a l .
and s h o r t ( c ) ,
E ither
The w r i t e r u s e d a
s c a l e r u l e h e ld f l u s h as p o s s i b l e to specimens f o r measuring r e s p e c t i v e
lengths o f th ese ax es„
Having r e c o r d e d a x i s
lengths to th e n e a re s t 0.05
i n c h , v a l u e s o f b / a and c / b w er e co mputed and p l o t t e d on a c h a r t
43) f o r a s i n g l e s p h e r i c i t y value-.
(Figure
These s p h e r i c i t y v a lu e s f o r a l l f i f t y
s p e c i m e n s w e r e t h e n a v e r a g e d f o r a mean s p h e r i c i t y v a l u e f o r t h e e n t i r e
sample.
A l t h o u g h Krumbein (194 1) a d v o c a t e d u s i n g s p e c i m e n s o f a s i n g l e
s iz e range in th e determ in atio n s of s p h e r i c it y ,
t h i s was deemed i m p o s s i b l e
due t o t h e co mp le x n a t u r e o f t h e d e p o s i t s .
Method o f d e t e r m i n i n g r o u n d n e s s
To d e t e r m i n e r o u n d n e s s ,
s p e c i m e n s w e r e compared v i s u a l l y w i t h s i l ­
h o u e t t e s ( F i g u r e 42) o f known r o u n d n e s s i
I f w e a t h e r i n g had p r o d u c e d a
f r e s h f a c e t w hi ch had o b v i o u s l y o c c u r r e d s i n c e d e p o s i t i o n o f t h e s p e c i m e n ,
45
r o u n d n e s s was d e t e r m i n e d f o r t h e p r e - e x i s t i n g form and t h e s p e ci m en was
t a l l i e d as " f r e s h l y broken".
Size o f p a r t i c l e s
The f i g u r e u s e d a s mean o f maximum d i a m e t e r was o b t a i n e d by a v e r a g i n g
t h e maximum d i a m e t e r o f a l l p e b b l e s c o l l e c t e d i n t h e s a m p l e .
Composition
The c o m p o s i t i o n o f e a c h s pe ci m en was n o m i n a l l y r e c o r d e d .
one s e d i m e n t a r y s u i t e i s p r e s e n t i n t h e a r e a ,
t h e most p a r t o n l y two i g n e o u s r o c k t y p e s ,
Since only
t h e F o r t Union r o c k s ,
d i o r i t e and t h e r a l i t e ,
and f o r
this
p r e s e n t e d no g r e a t d i f f i c u l t y .
D iscussion o f th e graphs
On t h e f o l l o w i n g f o u r g r a p h s 6 t h e h o r i z o n t a l d i r e c t i o n
( m i l e s from
da tum ") was c a l c u l a t e d i n t h e f o l l o w i n g m an ne r: t h e d i s t a n c e from t h e sam­
p l e t o t h e 8000 f o o t c o n t o u r - l i n e on t h e main m ou n ta in f r o n t was m ea s ur ed
in a s t r a i g h t
l i n e p r o v i d e d t h a t no o b s t a c l e s t o o d b e tw e en t h e tyro.
I f an
i s o l a t e d o b s t a c l e o v e r 8000. f e e t i n t e r v e n e d , t h e s h o r t e s t p o s s i b l e d i s t a n c e
around, i t t o t h e 8000 f o o t c o n t o u r was c a l c u l a t e d i n s t e a d .
1
The a d v a n t a g e o f u s i n g such a "phantom datum" l i e s i n t h e f a c t t h a t
i t p r o v i d e d a common b a s i s f o r a l l t h e s u r f a c e s a l l o w i n g c o m p a r i s o n s on
t h e same g r a p h s . -
I f a datum su ch a s t h e " h e a d o f t h e s u r f a c e " had been
u s e d , t h e r e wou ld be no v a l i d b a s i s f o r c o m p a r i s o n .
Pl u m l e y ( 1 948 ) showed t h a t i n many p r e s e n t - d a y s t r e a m s t h e w e i g h t o f
sediment load d e c re a s e s e x p o n e n ti a l l y as a f u n c tio n o f d i s t a n c e ,
according
46
F ig u re 22.
I n d e x map showing l o c a t i o n o f s a m p l e s u s e d i n t h e s t a t i s t i c a l
studies.
The l o c a t i o n s o f t h e s u r f a c e s and t h e m a j o r d r a i n a g e s a r e a l s o
shown.
47
t o S t e r n b e r g ' s Law, W=Wq e“ *£x wher e W e q u a l s t h e w e i g h t a t any p o i n t „ Wq
e q u a l s t h e i n i t i a l w e i g h t , x e q u a l s t h e d i s t a n c e and k e q u a l s t h e c o e f f i ­
c i e n t o f weight r e d u c t i o n „
The e x p o n e n t i a l n a t u r e o f t h i s f u n c t i o n r e ­
q u i r e s t h a t t h e d a t a p l o t a s a s t r a i g h t l i n e on s e ra i lo g p a p e r , where
d ista n c e is th e independent v a r i a b le .
that sphericity,
roundness,
and s i z e ,
I t was f o u n d f o r t h e p r e s e n t s t u d y ,
a l l fu n ctio n s o f abrasion, also follow
v a r i a t i o n s o f S t e r n b e r g ' s Law and t h e y t o o p l o t a s s t r a i g h t
lo g p a p e r .
l i n e s on se rai -
B e s t r e s u l t s w er e o b t a i n e d a l s o by u s i n g s e m i l o g p a p e r t o p l o t
t h e c o m p o s i t i o n c u r v e s ■„
48
SPHERICITY
VS.
DISTANCE
/.0 0 0
O* 9 0 0
. •
I
4-> 0 - 7 0 0
. -
O
•M
I
0)
JC
co
*
—
a z r^ - r -
U
^
•
*
0 ,6 0 0
O -S -OO
0
2
4
6
Q
1
0
/
2
M i l e s from datum
F i g u r e 2 3 . On t h e abov e g r a p h , Roman n u m e r a l s i n d i c a t e s u r f a c e d e s i g n a ­
tion.
E x c e p t f o r s u r f a c e s I and I I , s p h e r i c i t y shows a t e n d e n c y t o i n ­
c r e a s e w i t h d i s t a n c e t r a n s p o r t e d from t h e m o u n t a i n s . The c u r v e s f o r
s u r f a c e s I I I n and I l l s a r e n e a r l y p a r a l l e l w h i l e t h e c u r v e f o r s u r f a c e
IV i s s t e e p e s t .
The most i n t e r e s t i n g f e a t u r e o f t h i s g r a p h i s t h e
downward s l o p e o f t h e c u r v e f o r s u r f a c e I .
The datum from whi ch d i s ­
t a n c e s a r e m e a s u r e d i s t h e 8000 f o o t c o n t o u r ( s e e pa g e 4 5 ) .
49
COMPOSITION VS. DISTANCE
M i l e s from datum
F i g u r e 24.
The p e r c e n t a g e o f c r y s t a l l i n e r o c k s e x p r e s s e d a s a f r a c t i o n
o f t h e t o t a l g r a v e l c o v e r , d e c r e a s e s w i t h d i s t a n c e from t h e datum e x c e p t
f o r s u r f a c e I where t h e y i n c r e a s e w i t h d i s t a n c e .
P o ssib le explanations
f o r t h i s a p p a r e n t l y an om al o u s s i t u a t i o n w e r e i n c l u d e d i n t h e d i s c u s s i o n
of surface I.
The datum from wh ic h d i s t a n c e s a r e m e a s u r e d i s t h e 8000
fo o t c o n to u r ( s e e page 4 5 ).
50
ROUNDNESS VS. DISTANCE
0700
0 .6 0 0
C L
JZZT/7 __ —
—
0.5 0 0
____ S rL
JZ—
CO
-
--------
0.400
C
73
C
3
C
Cti
6.300
o.zoo
O
2
4
6
M il e s from datum
3
/o
12
F i g u r e 25.
The c u r v e f o r s u r f a c e I i s downward i n d i c a t i n g d e c r e a s i n g
r o u n d n e s s w i t h d i s t a n c e from t h e datum .
E x c e p t f o r m in o r v a r i a t i o n s ,
t h e o t h e r f o u r c u r v e s a r e c o m p a r a b l e , t h e c u r v e f o r s u r f a c e IV b e i n g
s l i g h t l y s te e p e r than the o t h e r s .
F i g u r e 26 .
The g r a p h on t h e f o l l o w i n g p a g e , showing s i z e v e r s u s d i s t a n c e ,
i s s t r i k i n g in t h a t th e curves s h i f t in slo p e in a clockw ise d i r e c t i o n
from o l d e s t t o y o u n g e s t . S i z e i n c r e a s e d m a r k e d l y w i t h d i s t a n c e f o r s u r ­
f a c e I and s l i g h t l y f o r s u r f a c e I I .
The r e m a i n i n g t h r e e c u r v e s s l o p e a t
i n c r e a s i n g l y s t e e p a n g l e s showing d e c r e a s e o f s i z e w i t h d i s t a n c e t r a n s ­
ported.
Thes e r e l a t i o n s h i p s a r e i n t e r e s t i n g , and t h e y may i n d i c a t e
r e l a t i v e l y c o n t i n u o u s c h a n g e s i n t h e e n v i r o n m e n t o v e r lo n g p e r i o d s o f
tim e.
P e r h a p s t h e d i s s e c t i o n o f t h e m o u n ta in r a n g e which has l e d t o ex p o ­
s u r e o f g r e a t e r and g r e a t e r amounts o f c r y s t a l l i n e r o c k s a c c o u n t s f o r t h e s e
r e l a t i o n s h i p s . The l a r g e r amounts o f c r y s t a l l i n e g r a v e l s b e i n g t r a n s ­
p o r t e d on s u c c e s s i v e l y y o u n g e r s u r f a c e s e s p e c i a l l y n e a r and w i t h i n t h e
m o u n t a i n r a n g e would c a u s e t h e a v e r a g e s i z e o f t h e g r a v e l s n e a r t h e moun­
t a i n s t o be c o n s i d e r a b l y l a r g e r t h a n f u r t h e r away from t h e m o u n t a i n s .
The d i s c u s s i o n on p a g e s 18 t o 22 o f t h e g r a v e l s on s u r f a c e I i s p e r t i n e n t
to t h i s d i s c u s s i o n .
ean o f maximum d i a m e t e r s ( i n c h e s )
51
S IZ E VS. DISTANCE
M i l e s from datum
52
STREAM AND DRAINAGE CHARACTERISTICS
Introduction
The o v e r a l l d r a i n a g e p a t t e r n shows a r e m a r k a b l e d e g r e e o f u n i f o r m i t y .
In p a r t i c u l a r ,
Cot to n wo o d and Rock C r e e k s a r e n e a r l y p a r a l l e l t h r o u g h o u t
much o f t h e i r c o u r s e s .
the Shields River;
sid es„
Other,
Both bend s o u t h w a r d a t c o m p a r a b l e d i s t a n c e s from
b o t h h a v e a d e c i d e d l a c k o f t r i b u t a r i e s on t h e i r s o u t h
s m a l l e r s t r e a m s su ch a s To b in and F a l l s C r e e k s f o l l o w s i m i ­
l a r southw esterly ro u te s.
the area,
Ho rs e C r e e k ,
in t h e extreme n o r th e r n p a r t o f
i n c o n t r a s t t o a l l o t h e r s t r e a m s , has a b r o a d f l a t v a l l e y and
flows n e a r l y s t r a i g h t w e st.
In p l a n ,
Creek,
at le a s t,
Rock C r e e k i s v e r y n e a r l y i d e n t i c a l t o Cottonwood
b u t when t h e d e t a i l s a r e e xa mi ned , t h e d i f f e r e n c e s a r e c o n s i d e r a b l e .
Sheep C r e e k ,
b e f o r e i t was d i v e r t e d by a s m a l l p a t c h o f m o r a i n e ,
fl o w e d
s t r a i g h t s o u t h i n t o Rock C r e e k t h r o u g h t h e v a l l e y o f what i s now an i n t e r ­
m i t t e n t s t r e a m c o m p l e t i n g t h e p l a n o f a c o n t i n u o u s s t r e a m t h a t was a n e a r l y
p e r f e c t r e p l i c a o f Cot to n wo o d C r e e k moved s o u t h w a r d .
I t seems q u i t e l i k e l y t h a t Cot to nw oo d and Rock C r e e k s h a v e fl o w e d
more n e a r l y due w e s t i n t h e p a s t ,
present p o in ts.
e n t e r i n g t h e S h i e l d s R i v e r n o r t h o f tfye
T h i s s u g g e s t s a s h i f t i n g o f t h e d r a i n a g e to t h e s o u t h .
Cot to nw o od C r e e k c o u l d n o t ha ve s h i f t e d fro m t h e n o r t h s i n c e t h e e s t a b l i s h ­
ment o f s u r f a c e I I I ,
b u t i t v e r y l i k e l y f l o w e d on s u r f a c e I I I and h e l p e d t o
carve the su rfa c e.
Cot to nw o od C r e e k
Cot to n wo od C r e e k ,
l a b e l e d " P i n e Gr e e k " on o l d e r maps, h a s i t s o r i g i n
53
f i v e m i l e s n o r t h o f t h e mapped a r e a .
w ater th e y e a r round,
I t c a r r i e s a s u b s t a n t i a l volume o f
enough t o i r r i g a t e much o f t h e s u r r o u n d i n g l a n d .
The
u p p e r r e a c h e s o f t h e v a l l e y were g l a c i a t e d a t l e a s t t w i c e ; b o t h t i m e s i c e
e x tended f u r t h e r south than Ibex M ountain,
T h r o u g h o u t mo st o f i t s c o u r s e ,
C ot to n w oo d C r e e k f l o w s i n a d e e p c a n y o n - l i k e v a l l e y w i t h v e r y l i t t l e
plain,
flood-
The n o r t h s i d e o f t h i s v a l l e y i s w a s t i n g a t a m o d e r a t e r a t e w h i l e
t h e s o u t h s i d e i s q u i t e s t a b l e i n most p l a c e s ;
e r l y dip of bedrock.
Several m oderately la rg e ,
a consequence o f th e n o r th ­
recent landslide scars lin e
th e n o r th s id e o f th e v a l l e y about f i v e m ile s n o r th e a s t o f Clyde Park,
a few a c t i v e slumps a r e p r e s e n t .
o f Elk M ountain,
S tatistical
and
The same c o n d i t i o n s e x i s t j y s t n o r t h e a s t
s t u d i e s o f t h e g r a v e l s b e i n g t r a n s p o r t e d by
Co tt o n w o o d C r e e k w e r e u n d e r t a k e n a t two l o c a t i o n s a b o u t f i v e m i l e s , a p a r t
(see A p p e n d i x A ) ,
T h e s e s t u d i e s i n d i c a t e d marked i n c r e a s e s i n b o t h s p h e r i ­
c i t y a nd r o u n d n e s s i n t h e d i r e c t i o n o f t r a n s p o r t .
The a v e r a g e s i z e o f t h e
g r a v e ls being t r a n s p o r t e d decreased w ith d i s t a n c e .
Elk Mountain,
In t h e v i c i n i t y o f
s e v e r a l s p r i n g s o c c u r a l o n g t h e n o r t h w a l l o f Cot to nw oo d
Creek,
Rock C r e e k
Rock C r e e k o r i g i n a t e s a b o u t t w o m i l e s n o r t h o f t h e mapped a r e a „
Through most o f i t s
l o w e r r e a c h e s , Rock C r e e k o c c u p i e s a s h a l l o w v a l l e y
b u t from a b o u t t h r e e m i l e s s o u t h o f E l k M o u n ta in t o w h e r e i t
leaves the
m o u n t a i n s t h e s l o p e s a r e s t e e p and t h e s t r e a m i s i n t h e p r o c e s s o f w i d e n i n g
t h e v a l l e y f l o o r by l a t e r a l p l a n a t i o n ,
Above wh er e t h e s t r e a m l e a v e s t h e
m ountains i t flow s in a b e a u t i f u l "D-shaped" v a l l e y .
B
C
D
F i g u r e 27.
Panorama t a k e n n o r t h o f Cottonwood C r e e k i n s e c t i o n 7, T. 2 N . , R. 10 E.
View i s t o t h e
w e s t o v e r t h e v a l l e y o f Cot to nw oo d C r e e k .
The s u r f a c e i n t h e f o r e g r o u n d (C) on t h e r i g h t i s IV and
t h a t j u s t a bo ve i t i s I I I ( D ) .
In c o n t r a s t t o t h e s o u t h s i d e o f t h e v a l l e y , t h e n o r t h s i d e i s
su b je c t to frequent la n d s lid e s .
Squa w's T i t i s i n t h e d i s t a n c e on t h e l e f t a t A. At B i n t h e
d i s t a n c e i s t h e B r i d g e r Range.
55
RocIc C r e e k i s c a r r y i n g a he a v y l o a d o f g r a v e l b o t h by v i r t u e o f t h e
w a s t i n g s i d e s and s u p p l y o f d i o r i t e from f u r t h e r s o u r c e s i n t h e m o u n t a i n s „
In p la c e s th e stream i s b r a id in g ,
e s p e c i a l l y n e a r and w i t h i n t h e m o u n t a i n s „
Rock C r e e k i s a p p a r e n t l y g r a d e d i n t h e s e n s e t h a t i t
downcutting, but r a t h e r i t
widening i t s
is not extensively
is c u ttin g l a t e r a l l y into th e v a lle y ,w a lls
f l o o d p l a i n and t h e r e b y i n i t i a t i n g p e d i m e n t f o r m a t i o n .
This
w i l l b e d i s c u s s e d i n more d e t a i l l a t e r i n t h i s p a p e r .
Other. S t re a m s
The s m a l l ,
i n s e q u e n t s t r e a m s n o r t h o f Cottonwood C r e e k which a r e
d i s s e c t i n g s u r f a c e I I I i a r e p r o d u c t s o f he a d wa rd e r o s i o n from t h e S h i e l d s
River,
The b r o a d ,
F o r t Union and i t
f l a t v a l l e y o f Ho rs e C r e e k f o l l o w s t h e s t r i k e o f t h e
i s c o n s i d e r a b l y l a r g e r t h a n one would e x p e c t o f su ch a
s m a l l s t r e a m a s Ho rs e C r e e k ,
( t e r m e d " H o r s e f l y C r e e k " on o l d e r m a p s ) , a l ­
t h o u g h t h e w a t e r t a k e n from t h e c r e e k f o r i r r i g a t i o n p u r p o s e s may make t h e
stream appear sm a lle r than i t r e a l l y i s .
The t r u n c a t e d d i k e s o u t h e a s t o f
I b e x M ou n ta in ( s e e F i g u r e 4 ) , m i g h t h a v e had d r a i n a g e d i r e c t e d o v e r i t a t
one t i m e i n t o H o r s e C r e e k , p r o b a b l y d u r i n g t h e e a r l i e r o f t h e two g l a c i a l
advances,
thereby accounting fo r the o v ersized v a lle y ,
Hammond C r e e k ' s p i c t u r e s q u e v a l l e y i n s e c t i o n s 6,
12 and I j u s t e a s t
o f E l k M ou n tai n i s bo unded on t h e n o r t h w e s t by t h e c u e s t a - l i k e c l i f f s o f
F o r t Union and on t h e s o u t h e a s t by t h e s l o p e s r e g r a d e d fro m s u r f a c e I ,
v a l l e y , which f o l l o w s t h e s t r i k e o f t h e F o r t Union f o r t h e most p a r t ,
The
is
c u t from 400 t o 500 f e e t b e l o w s u r f a c e I , t h e n o r t h s l o p e s b e i n g s t e e p e s t .
The s m a l l ,
i n t e r m i t t e n t s t r e a m s b e tw e en Cottonwood and Rock C r e e k s ,
56
e s p e c i a l l y s o u t h and w e s t o f E l k M o u n t ^ n ^ , a r e p r i m a r i l y c o n s e q u e n t a n d
n e a r l y a l l o f them f l o w t o w a r d B o c k / C r e e k .
S o u t h o f Rock C r e e k , t h e
d r a i n a g e i s p r e d o m i n a n t l y c o n s e q u e n t r e w a r d —t h e ^ o u t h and s o u t h w e s t „■ The
exception i s F a l l s Creek,
e s p e c i a l l y where i t flows through th e canyon.
Here, F a l l s Creek i s superim posed.
Throughout th e rem ainder o f i t s C oursej
ho we ve r, i t h a s v e r y l i k e l y s h i f t e d d i r e c t i o n c o n s i d e r a b l y ^
The due wes t
c o u r s e o f F a l l s C r e e k t h r o u g h t h e c a n y o n s u g g e s t s t h a t i n t h e p a s t i t may
ha ve e n t e r e d t h e S h i e l d s t o t h e n o r t h o f i t s p r e s e n t m ou th .
I t has t h e r e ­
f o r e s h i f t e d i t s c o u r s e t o t h e s o u t h , p e r h a p s as a r e a c t i o n t o t h e same
i n f l u e n c e wh ic h h a s c a u s e d Rock C r e e k and Cot to n wo o d C r e e k t o bend t o t h e
south.
The S h i e l d s R i v e r f l o o d p l a i n a v e r a g e s n e a r l y a h a l f - m i l e w i d e .
most p l a c e s ,
Th
t h e r i v e r i s f l o w i n g on v a l l e y f i l l o f u n d e t e r m i n e d d e p t h .
It
i s m e a n d e r i n g e x t e n s i v e l y on t h e f l o o d p l a i n a n d t h e r e a r e a few oxbow l a k e s
whic h h a v e b e e n c u t o f f from t h e r i v e r .
The v a l l e y s h o u l d p r o b a b l y be
c l a s s e d a s m a t u r e s i n c e t h e meander b e l t e q u a l s t h e w i d t h o f t h e f l o o d plain.
The l o a d b e i n g s u p p l i e d t o t h e r i v e r by i t s e a s t e r n t r i b u t a r i e s i s
m o d e r a t e l y l a r g e b u t I know n o t h i n g a b o u t t h o s e t h a t e n t e r from t h e w e s t .
A ccordingly,
is aggrading,
)
no c o n c l u s i v e s t a t e m e n t s c a n b e made as t o w h e t h e r t h e r i v e r
degrading or a t e q u ilib r iu m „
57
GLACIATION AND ITS CONSEQUENCES
Introduction
A l l o f t h e l a r g e v a l l e y s o f t h e C r a z y M o u n ta i n s s u p p o r t e d g l a c i e r s ,
some q u i t e l a r g e .
The m o u n t a i n s , ho wev er ,
l i e from 50 t o 60 m i l e s s o u t h
o f t h e a r e a c o v e r e d by c o n t i n e n t a l g l a c i a t i o n .
on t h e s o u t h and e a s t s i d e s o f t h e m o u n t a i n s .
ber,
S w e e t g r a s s and Big E l k C r e e k s had g l a c i e r s
The l a r g e s t g l a c i e r s were
Cot to nw oo d C r e e k , Big Tim­
10 t o 18 m i l e s in. l e n g t h ,
as i n d i c a t e d by t h e p o s i t i o n o f t h e m o r a i n a l d e p o s i t s
(M ansfield,
1 9 09 ) .
Local r a n c h e r s i n d i c a t e sm all g l a c i e r s a r e s t i l l p r e s e n t in t h e Crazy
M o u n ta i n s b u t I d i d n o t o b s e r v e th em .
A l l t h e h i g h e r v a l l e y s h a v e c i r q u e s a t t h e i r h e a d s ; many h a n g i n g
v a l l e y s a r e 600 f e e t o r more ab o v e t h e main v a l l e y f l o o r .
S t r i a e in th e
u pper p a r t s o f t h e l a r g e r canyons a r e c u t in th e hard ro ck s o f th e igneous
<
c o r e and c o n t a c t z o n e .
Beyond t h e h a r d r o c k a r e a , s t r i a e , i f p r e s e n t , a r e
o b s c u r e d by g l a c i a l and f l u v i a t i l e m a t e r i a l s which p a r t i a l l y f i l l t h e
canyons.
T e r m i n a l and l a t e r a l m o r a i n e s a r e fo u n d i n t h e l o w e r p a r t s o f t h e
l a r g e r canyons, but th e moraine i s u s u a lly not w ell d e fin e d near th e can­
yon h e a d s .
C o l l u v i u m , w h ic h o c c u r s a l m o s t e v e r y w h e r e , h a s m i n g l e d w i t h and
obscured the morainal m a te ria ls o f th e upper v a lle y s .
A ll o f the larger
strieani v a l l e y s o f t h e a r e a s o u t h w e s t o f t h e m o u n t a i n s ha v e w e l l d e f i n e d
d e p o s its o f moraine.
T h e r e h a v e b e e n a t l e a s t two m a j o r g a l c i a l a d v a n c e s i n t h e a r e a ,
o f wh ic h e x t e n d e d a s h o r t d i s t a n c e beyond t h e m o u n ta in f r o n t .
both
The e a r l i e s t
g l a c i a l a d v a n c e i s marked by s c a t t e r e d p a t c h e s o f s u bd ue d m o r a i n e ,
the
58
l i m i t s o f which a r e o f te n o b s c u re .
The most r e c e n t g l a c i a l a d v a n c e was
n o t so e x t e n s i v e a s t h e e a r l i e r o n e b e c a u s e f r e s h e r and y o u n g e r m o r a i n e
l i e s n e a r e r t h e p r e s e n t v a lle y s than th e o l d e r ,
more su b d u e d m o r a i n e .
The
most r e c e n t p e r i o d o f e x t e n s i v e g l a c i a l a c t i v i t y h a s l e f t d i s t i n c t b o d i e s
o f k e t t l e and kame m o r a i n e a s w e l l a s a r e a s o f g l a c i a l outwa'sh.
S t u d i e s o f t h e r e a l t i o n s h i p s b e tw e e n t h e m a j o r s u r f a c e s and t h e
g l a c i a l d e p o s i t s h as c o n t r i b u t e d a g r e a t d e a l t o w a r d an u n d e r s t a n d i n g o f
the h is to r y of the area.
Bock C r e e k V a l l e y G l a c i e r s
At l e a s t t w i c e ,
l a r g e v a l l e y g l a c i e r s i s s u e d from t h e u p p e r r e a c h e s
o f Rock C r e e k and e x t e n d e d a c o n s i d e r a b l e d i s t a n c e s o u t h w e s t w a r d .
Although
t r a c e s o f m o r a i n e 1from t h e f i r s t g l a c i a t i o n a r e few and i n many p l a c e s
obscure,
t h e e v id en ces o f th e l a t e s t g l a c i a l advance a r e a b u n d a n t.
Near Rock C r e e k ,
a l a r g e body o f m o r a i n e o f t h e most r e c e n t g l a c i a l
a d v a n c e i s f o u n d i n T 1 2 N. , R 1 11 E 1 ( s e e F i g u r e I ) .
northw estern corner of se ctio n
11.
I t begins in the
17 and e x t e n d s i n t o s e c t i o n s 8, 9,
10, and
In t h e n o r t h w e s t e r n c o r n e r o f s e c t i o n 17 and e x t e n d i n g o n l y a s h o r t
distance into
18,
a c c u r a t e l y mapped.
w ith a long,
it
is p r e s e n t as h i l l s ,
s e v e r a l o f them t o o s m a l l t o be
The l a r g e s t body o f m o r a i n e i s i n s e c t i o n s 8, 9 and 10
h ig h er r id g e o f t h i s m a te r ia l extending along th e southern
boundary o f t h e s e s e c t i o n s .
the youngest g l a c i a l i c e .
T h i s r i d g e marks t h e s o u t h e r n m o s t a d v a n ce o f
The s u r f a c e o f t h e m o ra i n e i s c o v e r e d w i t h r o c k s
and b o u l d e r s up t o t e n f e e t a c r o s s , a l o n g w i t h e v e r g r e e n ,
grass.
K e t t l e s a r e commonly c o v e r e d w i t h Aspen t r e e s .
sage,
and t h i c k
asm*
Ol
'O
F ig u re 28.
U- s h a pe d v a l l e y o f Rock C r e e k l o o k i n g n o r t h w a r d from s e c t i o n 10, I . 2 N1
R. 11 E.
La rg e body o f m o r a i n e i s in t h e f o r e g r o u n d .
I c e was o v e r 400 f e e t deep
i n t h i s v a l l e y , and i t hea ded b e h i n d t h e m o u nt a in a t A. N o t i c e t h e c i r q u e s .
60
The n o r t h s i d e o f Iiock C r e e k i n s e c t i o n s 8 and 9 i s v e r y s t e e p and no
moraine i s p r e s e n t ,
a l l o r n e a r l y a l l o f t h e d e b r i s a p p a r e n t l y h a v i n g been
d e p o s ite d south o f t h e c re e k .
a ridge,
is
In s e c t i o n 10, a n a r r o w c h a n n e l c u t s a c r o s s
th e southernmost m orainal f r o n t in t h e a re a .
The c h a n n e l , which
l i n e d w i t h w a t e rw o rn g r a v e l s , was c u t i n t h e m o r a i n e when t h e i c e was
still
behind t h e moraine,
and a p p a r e n t l y c a r r i e d a p a r t o f t h e m e l t w a t e r t o
L i t t l e Bock C r e e k d i r e c t l y t o t h e s o u t h .
The o n l y m ap p a b l e body o f m o r a i n e o f t h e e a r l i e r a d v a n c e a s s o c i a t e d
w i t h Bock C r e e k i s on s u r f a c e I I i n s e c t i o n 15, T. 2 N . , fi. 11 E. ( s e e
F i g u r e s I and 1 3 ) .
T h i s i s an a r e a o f su b d u e d r e l i e f which c o n t a i n s a h i g h
concentration of large,
p a r t i a l l y b u r i e d b o u l d e r s which h a v e u n d e r g o n e c o n -
s i d e r a b l y mure w e a t h e r i n g t h a n t h o s e common i n t h e f r e s h m o r a i n e .
o l d e r m o r a i n e l i e s on t h e s o u t h edg e o f t h e s u r f a c e .
Th is
It is equally proba­
b l e t h a t t h e m o r a i n e was d e p o s i t e d by a n e a r l y g l a c i e r i s s u i n g from t h e
w e s t f o r k o f Buck Creek".when t h e a r e a a t t h e hea d o f F a l l s C r e e k had n o t
yet reached i t s p resen t s t a t e of excavation.
In a d d i t i o n t o t h e p r e v i o u s l y d e s c r i b e d m o r a i n e ,
s e v e r a l small p a tc h e s
o f b o u l d e r s a r e p r e s e n t a l o n g t h e n o r t h e d g e o f s u r f a c e I I i n s e c t i o n s 15
and 16, T. 2 N., B. 11 E. e s p e c i a l l y i n t h e v a l l e y o f L i t t l e Bock C r e e k
s u g g e s t i n g d e p o s i t i o n by an e a r l y g l a c i e r i s s u i n g from Bock C r e e k Ca ny on .
Buck C r e e k V a l l e y G l a c i e r .
In t h e e x t r e m e e a s t e r n p a r t o f t h e a r e a i n s e c t i o n s
11,
12,
13, and
14 o f I.- 2 N , , R. 11 E. i s a c o n t i n u o u s body o f m o r a i n e w h ic h was d e p o s i t e d
by a g l a c i e r i s s u i n g from t h e v a l l e y o f t h e w e s t f o r k o f Buck C r e e k .
This
.
61
F i g u r e 29.
Ar e a o f m o r a i n e i n c e n t e r o f p i c t u r e , s e c ­
t i o n 5, T. 2 N . , R. 11 E . , w h ic h was d e p o s i t e d by Sheep
Creek G l a c i e r .
Duck M ou n tai n i n t h e b a c k g r o u n d .
Pho to
t a k e n from on t o p o f s u r f a c e I i n s e c t i o n 6.
F i g u r e 30 .
End m o r a i n e west o f Duck C r e e k m a r k i n g e x ­
t e n t o f Duck C r e e k G l a c i e r .
M o r a i n e was d e p o s i t e d from
t h e r i g h t . At B i n t h e b a c k g r o u n d i s Sheep M o u n t a i n .
In t h e f a r d i s t a n c e a r e t h e B e a r t o o t h and G a l l a t i n
Ranges.
The gap i s t h a t o f t h e Y e l l o w s t o n e R i v e r ( A ) .
62
m o r a i n e was d e p o s i t e d by t h e l a t e s t g l a c i e r wh ic h o c c u p i e d t h e v a l l e y ,
m o r a i n e o f t h e e a r l i e r advanc.e n o t b e i n g r e c o g n i z e d i n t h e a r e a .
The a r e a c o n s i s t s o f r u g g e d k e t t l e and kame t o p o g r a p h y ( s e e F i g u r e
32) whic h d i m i n i s h e s n o r t h w a r d a n d c u l m i n a t e s s o u t h w a r d i n a h i g h ,
horse­
s h o e - s h a p e d r i d g e ( s e e F i g u r e 30) b ey on d w h i c h d e p o s i t i o n was n e g l i g i b l e .
S o u t h o f t h i s r i d g e i s a smooth outwa.sh p l a i n ,
in s e c tio n s
13 a n d 14
e s p e c i a l l y smooth b e tw e e n A l d e r C r e e k and t h e w e s t f o r k o f Duck C r e e k .
Many b o u l d e r s i n t h e m o r a i n e r a n g e up t o t e n f e e t i n d i a m e t e r and
some o f them ha ve w e l l d e v e l o p e d s t r i a e
(see Figure 31).
The l a r g e s t b o u l d e r s
a r e d i o r i t e and some o f t h e s e c r y s t a l l i n e r o c k s a r e c h a t t e r m a r k e d .
s e c t i o n s 11 and 14, a t t h e e a s t e r n e x t r e m i t y o f s u r f a c e I I ,
l i e s d i s c o r d a n t l y upon t h e s u r f a c e ( s e e F i g u r e 3 2 ) .
the creek,
In
t h i s moraine
In s e c t i o n 13 e a s t o f
g l a c i a l d e p o s its o v e r l i e g e n tly n o r th e r ly dipping sedim entary
rocks.
The h i g h h i l l i n t h e c e n t e r o f s e c t i o n
b o u ld ers as w ell as water-worn g r a v e l s .
14 i s c a p p e d by c o a r s e a n g u l a r
The l a r g e b o u l d e r s s u g g e s t g l a c i a l
d e p o s i t i o n b u t i f s o , t h e y must r e p r e s e n t d e p o s i t i o n by a d i f f e r e n t ,
earlier
g l a c i e r t h a n t h a t which i s r e s p o n s i b l e f o r t h e d e p o s i t s j u s t t o t h e n o r t h ­
east.
I f t h is hypothesis is c o rre c t,
t h e e a r l i e r g l a c i e r was c o n s i d e r a b l y
l a r g e r and d e e p e r o r e l s e e r o s i o n was n o t n e a r l y so a d v a n c e d i n t h e a r e a
t h e r e b y a l l o w i n g t h e g l a c i e r t o f l o w on a h i g h e r l e v e l .
C ot to nw o od C r e e k V a l l e y G l a c i e r s
f
The r e l a t i o n s h i p s b e tw e en t h e two s e p a r a t e b o d i e s o f g l a c i a l d e p o s i t s
a r e b e s t shown e a s t o f I b e x Mo un tai n a l o n g Cot to nw oo d C r e e k ,
He re , two
F i g u r e 31 .
S t r i a t e d b o u l d e r fo und in
t h e m o r a i n e a s s o c i a t e d w i t h Duck
Creek.
T h i s b o u l d e r i s a b o u t 2% by
1% f e e t i n d i a m e t e r .
I t i s e x po s ed in
a f r e s h road cut along a logging t r a i l .
F i g u r e 32. T y p i c a l k e t t l e and kame to p o g r a p h y
i n t h e Duck Cr e e k m o r a i n e .
A
B
C
D
F i g u r e 33.
S u r f a c e I I (D) on t h e r i g h t , s u r f a c e I (A) on t h e l e f t s i d e o f t h e
shallow v a lle y .
L a t e r a l m o r a i n e o f Duck C r e e k G l a c i e r l i e s on t o p o f s u r f a c e
I I a t C and c o n t i n u e s t o t h e l e f t .
Duck Mountain i n t h e b a c k g r o u n d a t B.
h
65
very d i s t i n c t b odies o f moraine o f co m p le te ly d i f f e r e n t c h a r a c t e r a re ex ­
posed (se e F ig u re I ) .
The o l d e r m o r a i n e o c c u r s a b o u t a m i l e w e s t o f t h e
c r e e k from 100 t o 400 f e e t a b o v e t h e p r e s e n t c r e e k f l o o r w h e r e a s t h e y o u n g e r
m o r a i n e o c c u r s from c r e e k l e v e l up t o 300 f e e t ab o v e t h e v a l l e y f l o o r .
The d e p o s i t s a r e n e a r e r c r e e k l e v e l i n t h e n o r t h t h a n i n t h e s o u t h .
The
h i g h e s t p a r t s o f t h e o l d e r m o r a i n e t e n d t o be c o v e r e d and t h e y i n t e r m i n g l e
w i t h c o l l u v i a l d e p o s i t s from I b e x M o u n t a i n .
Cottonwood C r e e k h as c u t t o
bedrock through t h i s moraine in s e v e r a l p l a c e s .
F i g u r e 34.
Physiographic expression of the o ld ­
e s t o f t h e two g l a c i a l m o r a i n e s .
Notice the larg e
b o u ld e rs in the c e n te r o f t h e p i c t u r e .
66
The o l d e r , more s u b d u e d , m o r a i n e ( s e e F i g u r e s 34 and 35) h as a t e n ­
de nc y t o be swampy and v e r y p o o r l y d r a i n e d and a l t h o u g h t h e r e a r e o n l y a
few s u g g e s t i o n s o f k e t t l e s o r kames,
diam eter occur.
larg e boulders
ten
f e e t o r more i n
These l a r g e d i o r i t i c b o u ld e r s a re th o ro u g h ly weathered,
and o f t e n c r a c k e d i n s e v e r a l p i e c e s .
Although sm a lle r b o u ld e rs a re s c a rc e ,
s p o r a d i c p a t c h e s o f them o c c u r i n some o f t h e s h a l l o w v a l l e y s .
Rock C r e e k ,
As n e a r
t h e p r e s e n c e o f t h i s o l d e s t m oraine west o f t h e younger
m a t e r i a l s u g g e s t s t h a t g l a c i a t i o n was more w i d e s p r e a d d u r i n g t h e e a r l i e r
g l a c i a l advance than l a t e r .
F i g u r e 35 .
P h y s io g ra p h ic e x p re s s io n o f t h e moraine o f t h e e a r l i e r
a d v a n c e i n t h e f o r e g r o u n d w e s t o f Cot to n wo o d C r e e k . T h i s i s sub du ed ,
swampy l a n d w i t h some l a r g e b o u l d e r s .
The g l a c i e r came t o w a r d t h e
r i g h t out o f t h e a r e a in t h e c e n t e r o f th e p i c t u r e (A).
Notice the
l a n d s l i d e s c a r s a t B.
67
G l a c i a l d e p o s i t s o f t h e most r e c e n t a d v a n c e a r e l a r g e l y k e t t l e - k a m e
areas of large,
angular boulders,
w a t e r - w o r n c o b b l e s and l a r g e d e p o s i t s o f
g lacial flour.
In t h e s o u t h e r n p a r t o f t h e s e d e p o s i t s ,
kames t e n d t o be
e l o n g a t e d and d r u m l i n - l i k e i n t h e d i r e c t i o n o f g l a c i a l f l o w .
p r e s e n t on b o t h s i d e s o f t h e c r e e k b u t e a s t o f t h e c r e e k i t
less ex ten siv e.
M o ra in e i s
i s t h i n n e r and
Where t h e m o r a i n e r e s t s on s u r f a c e IV, i t g i v e s way t o
s e v e r a l s m a l l su b d u e d h i l l s
and t h e n t o o u t w a s h whi ch c a n n o t be a c c u r a t e l y
d e l i n e a t e d b e c a u s e i t m er g e s p e r f e c t l y w i t h t h e s u r f a c e .
q u i t e t h i n b u t no c u t s
I t a p p e a r s t o be
t h r o u g h i t w er e d i s c o v e r e d e x c e p t f o r some s h a l l o w
d i t c h e s which showed o b s c u r e g r a v e l p r o f i l e s .
Be c a u s e t h e h i g h e s t r e a c h e s
o f s u r f a c e IV a r e c o v e r e d by t h i s m o r a i n e , t h e p o s s i b i l i t y e x i s t s t h a t t h e
s u r f a c e was g r a d e d a t t h e t i m e t h e g l a c i e r d e p o s i t e d t h e m o r a i n e .
Nearly
i d e n t i c a l r e l a t i o n s h i p s b e tw e e n t h e o l d e r m o r a i n e and s u r f a c e I I I s u g g e s t
that
t h e same c o n d i t i o n s may be r e s p o n s i b l e f o r s u r f a c e I I I .
On t h e o t h e r h a n d , t h e same r e l a t i o n s h i p s a s d e s c r i b e d ab o v e migh t
i n d i c a t e t h a t s u r f a c e IV i s i n t e r g l a c i a l and s u r f a c e I I I i s o l d e r t h a n
e i t h e r g l a c i a l advance.
T h i s i s more p r o b a b l e b e c a u s e t h e m o r a i n e seems
t o r e s t d i s c o r d a n t l y on t h e s u r f a c e s .
O t h e r G l a c i a l F e a t u r e s and Summary
In s e c t i o n f i v e o f T. 2 N4, R. .11 E . ,
a small p a tc h o f r e c e n t moraine
( s e e F i g u r e s I and 29) h a s a l t e r e d t h e o r i g i n a l c o u r s e o f Sheep C r e e k .
S o u t h o f t h e m o r a i n e an i n t e r m i t t e n t s t r e a m l e a d i n g t o t h e M id d l e For k o f
Rock C r e e k a p p e a r s t o b e t h e o r i g i n a l c r e e k c o u r s e .
Creek, although i t
The v a l l e y o f Sheep
i s r a t h e r n a r r o w and s h a r p i n c r o s s s e c t i o n ,
is very
67a
The mo st r e c e n t c a n y o n mouth m o r a i n e o f t h e C r a z y M o u n ta i n a r e a
compares v e ry f a v o r a b l y w ith m oraine o f t h e P i n e d a l e ( l a t e W isconsin) su b ­
s t a g e o f g l a c i a t i o n o f n o r t h w e s t e r n Wyoming (Montague,
com m unication)„
p o o rly developed;
1962; p e r s o n a l
T h i s f r e s h m o r a i n e i s v e r y hummocky; d r a i n a g e w i t h i n i t
is
i t c o n t a i n s numerous s t r i a t e d b o u l d e r s and i t i s i n a
p o s i t i o n a d j a c e n t t o and a b o v e t h e p r e s e n t s t r e a m v a l l e y s .
The p r e c e d i n g
f a c t s a l l lead t o t h e c o n c lu s io n t h a t i t i s o f l a t e W isconsin age.
The r e l a t i o n s h i p s b e t w e e n t h e o l d e r a n d t h e y o u n g e r m o r a i n e i n d i c a t e
t h a t t h e o l d e r moraine i s e a r l y W isconsin.
Along C o tt o n w oo d C r e e k ( s e e
F i g u r e I) t h e o l d e r m o r a i n e l i e s o n l y a few f e e t a b o v e t h e l a t e W i s c o n s i n
m o r a i n e and i t o c c u p i e s a s i m i l a r p o s i t i o n w i t h r e s p e c t t o t h e s t r e a m .
This
i n d i c a t e s t h a t t h e g l a c i e r t h a t d e p o s ite d th e l a t e moraine followed e s se n ­
t i a l l y t h e same p a t h a s t h e e a r l i e r g l a c i e r .
I f a g r e a t i n t e r v a l o f tim e
had e l a p s e d b e t w e e n t h e d e p o s i t i o n o f t h e two, o n e would n o t e x p e c t t h e
stream t o reamin in such a com parable p o s i t i o n .
The v e r y s l i g h t d i f f e r e n c e
i n e l e v a t i o n b e t w e e n t h e two a r e a s o f m o r a i n e i n d i c a t e s t h a t e r o s i o n t h a t
o c c u r e d i n t h e i n t e r v a l o f t i m e b e t w e e n t h e i r d e p o s i t i o n was s l i g h t ;
c e r t a i n l y l e s s t h a n wo u ld b e e x p e c t e d f o r an e n t i r e i n t e r - g l a c i a l p e r i o d .
A l t h o u g h t h e o l d e r m o r a i n e i s c o n s i d e r a b l y more s u bd ue d t h a n t h e y o u n g e r ,
d rain a g e i s not w ell developed.
Even t h o u g h i t c a n n o t b e s t a t e d w i t h c e r t a i n t y ,
it
seems p r o b a b l e t h a t
t h e o l d e r m o r a i n e i s e q u i v a l e n t t o t h e B u l l Lake s t a g e o f n o r t h w e s t e r n
Wyoming, b u t a p r e - W i s c o n s i n a g e i s n o t i m p o s s i b l e b e c a u s e t h e amount o f
e r o s i o n may n o t n e c e s s a r i l y b e i n d i c a t i v e o f t h e l e n g t h o f t i m e t h a t h as
elapsed.
68
l i k e l y th e source o f t h i s patch o f m oraine,
No m o r a i n e o f t h e e a r l i e r
g l a c i a l a c t i v i t y was o b s e r v e d i n t h i s a r e a .
G enerally,
t h e m a j o r t o p o g r a p h i c f e a t u r e s o f t h e C r a z y M o u n ta in s
a p p e a r t o be p r e - g l a c i a l .
The i c e r e m a i n e d l o n g enough, ho we ve r, t o de ep en
and m o d if y t h e e x i s t i n g v a l l e y s and t o d e v e l o p t h e , c i r q u e s and a r e t e s com­
mon i n t h e h i g h e r m o u n t a i n s .
W i t h i n t h e a r e a a f f e c t e d by t h e g l a c i e r s ,
p o s t - g l a c i a l e r o s i o n has n o t a c c o m p l i s h e d much i n t h e way o f r e a d j u s t m e n t
of drainage.
Within t h e g l a c i a t e d a r e a ,
d rain ag e is very y o u th fu l but
beyond i t t h e r e h as be e n c o n s i d e r a b l e m o d i f i c a t i o n s i n c e g l a c i a l tim e*
CONCLUSIONS AND SUMMARY
Number and C a u s e s o f t h e E r o s i o n a l S t a g e s
I t c a n n e v e r b e u n e q u i v o c a l l y s t a t e d how many s e p a r a t e p e r i o d s o f
e r o s i o n t h e a r e a s o u t h w e s t o f t h e C r a z y M o u n ta i n s h a s u n d e r g o n e .
There
h a s be e n a t e n d e n c y i n p a s t s t u d i e s o f some Rocky M ou n tai n a r e a s t o p o s t u r
l a t e g r e a t numbers o f s t a g e s (Van TuyI and C o v e r i n g ,
s u r f a c e t h a t d o e s n o t seem t o match a n o t h e r .
1 9 3 5 ) ^ one f o r e v e r y
On t h e o t h e r han d, Wahlstrom
( 1 9 4 7 ) , w o r k i n g i n t h e same a r e a a s Van T u y l and C o v e r in g h a s c o n c l u d e d
that a single,
co n tinuous sequence o f e r o s i o n a l p ro c e s s e s has accomplished
t h e d i s s e c t i o n o f t h e C o l o r a d o F r o n t Ra n g e .
The p r e s e n c e o f r e m n a n t s o f numerous e r o s i o n s u r f a c e s a t d i f f e r e n t
l e v e l s h a s b e e n e x p l a i n e d by M e y e r h o f f and H u b b e l l (1928) a s a r e s p o n s e t o
i n t e r m i t t e n t v e r t i c a l u p l i f t s o f t h e r e g i o n s where t h e y o c c u r .
According
to t h i s treppen ( s t a i r ste p s) concept of m u ltip le erosion s u rfa c e s ,
u p l i f t i n t r o d u c e s a k n i c k p o i n t w hi ch t e n d s t o m i g r a t e u p s t r e a m .
e ach
Below t h e
69
k n i c k p o i n t t h e s t r e a m e r o d e s i t s bed t o w a r d a new b a s e - l e v e l i n t r o d u c e d by
u p lift„
W hil e a t t e m p t i n g t o a d h e r e t o t h e p h i l o s o p h y o f a s few e p i c y c l e s a s
possible,
I must n e v e r t h e l e s s c o n c l u d e t h a t t h e r e hav e bee n a t l e a s t f i v e
d i s t i n c t periods of erosion,
one f o r e a c h s u r f a c e p l u s t h e p r e s e n t o n e .
T h i s doe s n o t t a k e i n t o a c c o u n t e r o s i o n t h a t p r e c e d e d t h e c u t t i n g o f sur-?
face I.
I t seems p r o b a b l e t o o ,
s h o r t e r th an t h e e a r l i e r o n e s ,
that
t h e more r e c e n t e p i c y c l e s have been
because o f the r e l a t i v e l y small s iz e o f
s u r f a c e IV when co mpared ‘w i t h t h e p o s t u l a t e d f o r m e r e x t e n t o f s u r f a c e I
or II.
The f i v e e p i c y c l e s o f e r o s i o n may hav e r e s u l t e d from any o f s e v e r a l
possible causes.
I t seems a d v i s a b l e t o . a p p r o a c h t h e p r o b le m f r o m . a m u l t i ­
p le hypothesis view point,
P o ssib ilities
beginning w ith a l i s t i n g of th e p o s s ib le c a u se s.
include:
1) Sudden s pa sm o d i c l o w e r i n g o f t h e m a s t e r d r a i n a g e .
2) E r o s i o n c o n f i n e d t o s t r a t i g r a p h i c p l a n e s .
3) Change i n c l i m a t i c c o n d i t i o n s .
Sudden l o w e r i n g o f t h e m a s t e r d r a i n a g e ,
repeated s e v e ra l tim e s , p e r­
h a p s as a r e s u l t o f t e c t o n i c c h a n g e s some d i s t a n c e away, would c a u s e s t r e a m s
o f t h e a r e a t o r e a c t soon t h e r e a f t e r .
K n i c k p o i n t s m ig h t form i n i t i a l l y ,
b u t I do n o t b e l i e v e t h e y w ou ld be l o n g - l i v e d i n t h i s a r e a o f r e l a t i v e l y
e a s ily e ro d ib le sedim ents.
and would b e g i n
Instead,
t h e s t r e a m would c e a s e t o be g r a d e d
to c u t down, j u s t as Cot to nw oo d C r e e k i s now d o i n g ,
a new b a d e l e v e l .
When t h i s b a s e l e v e l was r e a c h e d ( a s i t
t o w a rd
i s f o r much o f
70
Sock C r e e k ) ,
t h e s t r e a m wou ld m i g r a t e l a t e r a l l y ,
with r e l a t i v e l y less
downcutting,
s i m i l a r t o c o n d i t i o n s a l o n g Rock C r e e k ,
B e c a u s e s t r a t i g r a p h i c p l a n e s do n o t p a r a l l e l s u r f a c e s i n t h e a r e a ,
t h e p o s s i b i l i t y o f s t r i p p e d p l a n e s ne e d n o t be c o n s i d e r e d i n d e t a i l .
f e r e n t i a l e ro sio n has,
D if­
ho wever, p l a y e d an i m p o r t a n t r o l e i n s h a p i n g t h e
C r a z y M o u n ta i n s p r o p e r .
A change in th e c l i m a t i c c o n d it io n s ,
intensity,
e s p e c i a l l y in th e p r e c i p i t a t i o n
ca n a c c o m p l i s h t h e same r e s u l t s a s t e c t o n i c movement.
c h a n g e from h e av y p r e c i p i t a t i o n
Thus, a
t o a l e s s e r amount migh t c a u s e d o w n c u t t i n g
to c e a s e and l a t e r a l p i a n a t i o n t o b e g i n .
The r e d u c e d s t r e a m volume c o u p l e d
w i t h t h e d e c r e a s e d amount o f e r o s i o n - r e t a r d i n g v e g e t a t i o n would c a u s e t h e
g r a v e l l o a d t o become, t o o g r e a t t o be t r a n s p o r t e d and t h e s t r e a m would
braid,
a c o n d itio n conducive to l a t e r a l p i a n a t io n or a g g ra d a tio n r a t h e r
than dow ncutting.
C o n d itio n s a s s o c i a t e d with t h e advance o f g l a c i e r s ;
increased p re c ip ita tio n ,
colder tem peratures, e tc .,
would be more c on du ­
c i v e to d o w n c u t t i n g t h an l a t e r a l p i a n a t i o n s u g g e s t i n g t h a t t h e s u r f a c e s
would be fo rm ed d u r i n g i n t e r g l a c i a l p e r i o d s .
I I I and IV,
With r e f e r e n c e t o s u r f a c e s
t h i s r e a s o n i n g a p p e a r s t o be v a l i d .
e p o c h s m ig h t h a v e o c c u r r e d b e f o r e s u r f a c e s
E a r l i e r unknown g l a c i a l
I and I I w er e c u t „
Furthermore,
t h e p r e s e n c e o f l a r g e amounts o f i c e and snow i n t h e m o u n t a i n s would t e n d
t o p r o t e c t t h e r o c k s t h e r e b y d e c r e a s i n g t h e d o w n c u t t i n g power o f t h e
stream s.
I f a v o r a sequence o f e v e n ts s i m i l a r to t h a t o u t l i n e d above.
present area,
ho wever ,
In t h e
s i n c e d e g r a d a t i o n h a s been g o i n g on a t l e a s t s i n c e
P lio c e n e tim e, c li m a t ic changes alo n e probably a r e in ad e q u a te to ex p la in
TI
a l l th e preceding r e l a t i o n s h i p s .
tion is th at at
An a l t e r n a t i v e t o t h e c l i m a t i c e x p l a n a ­
l e a s t p a r t o f t h e d e g r a d a t i o n r e s u l t e d from s t r e a m r e j u ­
v e n a t i o n due t o u p l i f t o f t h e e n t i r e a r e a d u r i n g l a t e T e r t i a r y and Q u a t e r ­
nary tim e.
Methods o f S u r f a c e C o n s t r u c t i o n
Each s u r f a c e , w i t h t h e p o s s i b l e e x c e p t i o n o f s u r f a c e IV,
fits
the
g e n e r a l d e s c r i p t i o n o f a p e d i m e n t i n t h a t e ach has been c u t a c r o s s t i l t e d
b e d r o c k and h as o n l y a r e l a t i v e l y t h i n g r a v e l c o v e r .
abut ag ainst
Two o f t h e s u r f a c e s
t h e m o u n t a i n f r o n t and t h e l o n g i t u d i n a l p r o f i l e s o f a l l a r e
concave upward.
S u r f a c e IV i s q u i t e n a r r o w r e l a t i v e t o i t s
i n g o r i g i n as a s t r e a m t e r r a c e .
The c l i m a t e s u n d e r which t h e s e s u r f a c e s
fo rm ed ha s n o t been u n e q u i v o c a l l y a s c e r t a i n e d ,
v a n c e d on p a g e 70 i s c o r r e c t ,
length su g g est­
but i f th e h ypothesis ad­
t h e y w er e form ed d u r i n g t h e r e l a t i v e l y d r y
in te rg la c ia l periods.
The manner i n which Rock C r e e k i s now w i d e n i n g i t s v a l l e y i n s e c t i o n
18 o f T, 2 N. , R. 11 E. may be c h a r a c t e r i s t i c o f how t h e s u r f a c e s were
formed.
H e re , t h e c h a r a c t e r o f t h e c a n yo n i s d i s t i n c t i v e .
t h e c an yon a r e shown i n f i g u r e s 39 and 4 0 .
P ro file s across
The wide v a l l e y f l o o r i s e x ­
p e c t a b l e f o r a s t r e a m f l o w i n g on a g e n t l e g r a d i e n t and m e a n d e r i n g o v e r much
of the floodplain.
150 f e e t p e r m i l e ,
the v alley .
Rock C r e e k ,
ho wev er ,
i s f l o w i n g on a g r a d i e n t o f a b o u t
s t e e p enough t o c a u s e s e v e r a l r a p i d s t o be p r e s e n t i n
Where i t
is not braid in g ,
one-tw entieth th a t of the v alley flo o r,
t h e width o f th e stream i s about
and i t m a i n t a i n s a r e l a t i v e l y
s tr a ig h t course g en erally diagonally across the valley.
72
The n o r t h w a l l s o f t h e canyo n a r e m a s s - w a s t i n g a t a r a p i d r a t e h e r e .
An o l d c a n a l which o n c e f lo w e d a l o n g t h e r i m o f t h e canyo n has been o b l i t e r a ­
t e d i n l a r g e p a r t by c r e e p ,
s i d e o f t h e canyo n i s
relationships,
Erosion i s ,
it
l a n d s l i d e s and s u r f a c e e r o s i o n .
l a n d s l i d i n g too,
f he s o u t h
but because of s c a rp -slo p e d ip -slo p e
i s n o t d o i n g so a t as r a p i d a r a t e as t h e n o r t h s i d e .
o f c o u r s e , most r a p i d a t t h e p o i n t s where t h e s t r e a m i s i n c o n ­
t a c t with the v a lle y w a ll,
u n d e r m i n i n g and rem o v in g t h e m a t e r i a l .
Hock
C r e e k ' s ban ks a r e a b o u t f o u r f e e t ab ove t h e w a t e r l i n e and t h e y c o n s i s t o f
r o u n d e d d i o r i t i c b o u l d e r s and c o b b l e s w i t h o n l y s m a l l amounts o f se d im e n ­
ta r y cobbles
(see Figure 36).
The g r a v e l c o v e r , which m a i n t a i n s a u n i f o r m
t h i c k n e s s and i s q u i t e l e v e l on t h e s u r f a c e ,
dow ncutting markedly.
shows t h a t t h e s t r e a m i s n o t
As t h e s t r e a m m i g r a t e s a c r o s s t h e v a l l e y and r e m o v e s ,
F i g u r e 36 . R e l a t i v e l y l e v e l r o c k - t e r r a c e t y p i c a l o f
t h e v a l l e y o f Rock C r e e k .
I t i s of uniform t h ic k n e s s
across the valley flo o r.
73
F i g u r e 37 .
View up Rock C r e e k .
S t re a m i s b r a i d i n g and
c u t t i n g i n t o t h e s o l i d b e d r o c k on t h e l e f t .
F i g u r e 30 .
B r a i d i n g c h a n n e l o f Rock C r e e k .
The s t r e a m
i s f l o w i n g r a p i d l y , c a r r y i n g a heavy l o a d , and u n a b l e
t o downcut b u t s t i l l c a p a b l e o f l a t e r a l p l a n a t i o n .
74
by l a t e r a l p l a n a t i o n , b o t h o l d g r a v e l and p r e v i o u s l y u n a f f e c t e d v a l l e y w a l l s ,
it
leaves behind i t th e previous channels,
f i l l e d with f r e s h g r a v e l .
T he s e r e l a t i o n s h i p s s u g g e s t t h a t Rock C r e e k i s i n t h e p r o c e s s o f
forming a pedim ent.
I t has bee n v e r t i c a l l y r e j u v e n a t e d t o i t s p r e s e n t p o s i ­
t i o n and s i n c e r e a c h i n g t h a t p o s i t i o n and e s t a b l i s h i n g an e q u i l i b r i u m ,
wh ic h i t w i l l n o t c u t g r e a t l y ,
i t has p rec e d e d to s h i f t
b e lo w
i t s course l a t e r a l l y ,
sapping th e sid es of i t s canyon.
B r a i d i n g i s a s i g n o f an o v e r l o a d e d s t r e a m and t h e s u p p l y o f d e b r i s
to Rock C r e e k i s more t h a n enough t o c a u s e b r a i d i n g .
A stream th a t is
c a r r y i n g a h e av y l o a d w i l l n o t swin g i n smooth r e g u l a r c u r v e s ,
but r a t h e r
t h e d e b r i s w i l l b l o c k t h e c h a n n e l and t h e s t r e a m w i l l s p r e a d , , s e t t i n g up
c r o s s c h a n n e l s whi ch d i f f e r from common m e a n d e r s .
A he a v y l o a d f a v o r s
l a t e r a l p l a n a t i o n a t a g i v e n h o r i z o n n o t o n l y by p r e v e n t i n g e x c e s s i v e c u t ­
ting,
b u t a l s o by f a v o r i n g l a t e r a l d i s p l a c e m e n t t h r o u g h a c c u m u l a t i o n o f
d e b r i s a l o n g and w i t h i n
nels,
the c h a n n e l.
Because t h e r e a r e then s e v e r a l chan­
no one o f them n e e d s h i f t v e r y f a r i n o r d e r t h a t l a t e r a l p l a n a t i o n
may t a k e p l a c e o v e r much o f t h e v a l l e y .
The c o n d i t i o n s p r e s e n t i n Rock C r e e k v a l l e y t h e r e f o r e ,
adequate to produce pediments but i t
are certain ly
i s d o u b tf u l whether such c o n d it io n s
alo n e could ever extend the s u rf a c e over extrem ely la rg e a r e a s .
not in v a lid a te the th eo ry ,
b u t i t does r e q u i r e e x p l a n a t i o n ,
T h i s d oe s
Howard (1942)
has p o i n t e d o u t t h a t s m a l l s t r e a m s p l a y a s i m p o r t a n t a r o l e i n l a t e r a l
p l a n a t i o n as t h e l a r g e r o n e s .
The t r i b u t a r i e s o f su ch a s t r e a m a s Rock
C r e e k w i l l become g r a d e d t o t h e c r e e k and t h e same p r o c e s s e s a s d e s c r i b e d
a bo ve w i l l a p p l y t o th em .
These s m a lle r s tre a m s,
although they appear to
75
f l o w on s t e e p e r g r a d i e n t s t h a n t h e l a r g e r s t r e a m s s uc h a s Rock C r e e k ,
are
n e v e r t h e l e s s g r a d e d t o t h e l a r g e r s t r e a m s and h e n c e t o t h e same b a s e l e v e l
and e v e n t u a l l y ,
t h e e n t i r e system should evolve i n t o a s i n g l e s u r f a c e o f
considerable extent.
As a f i n a l n o t e on t h i s
G i l b e r t ( 1 87 7)
subject,
t h e f o l l o w i n g q u o t a t i o n from
seems p e r t i n e n t :
" I t h a s be e n shown i n t h e d i s c u s s i o n o f t h e r e l a t i o n s o f
t r a n s p o r t a t i o n and c o r r a s i o n t h a t downward wear c e a s e s
when t h e l o a d e q u a l s t h e c a p a c i t y f o r t r a n s p o r t a t i o n .
Whenever t h e l o a d r e d u c e s t h e downward c o r r a s i o n t o l i t ­
t l e o r n o t h i n g , l a t e r a l c o r r a s i o n becomes r e l a t i v e l y and
a c t u a l l y of im portance.
The f i r s t r e s u l t o f t h e w e a r i n g
of the w a lls o f a s tr e a m 's channel i s th e form ation of a
floodplain.
As an e f f e c t o f momentum t h e c u r r e n t i s a l ­
ways s w i f t e s t a l o n g t h e o u t s i d e o f a c u r v e o f a c h a n n e l ,
and i t i s t h e r e t h a t t h e w e a r i n g i s p e r f o r m e d ; w h i l e a t
t h e i n n e r s i d e o f t h e c u r v e t h e c u r r e n t i s so s lo w t h a t
p a r t of the load i s d e p o site d .
In t h i s way, t h e w i d t h
Of t h e c h a n n e l r e m a i n s t h e same w h i l e i t s p o s i t i o n i s
s h i f t e d , and e v e r y p a r t o f t h e v a l l e y which i t h as c r o s s e d
i n i t s s h i f t i n g s comes t o be c o v e r e d by a d e p o s i t which
do es n o t r i s e ab ov e t h e h i g h e s t l e v e l o f t h e w a t e r .
The
s u r f a c e o f t h i s d e p o s it i s hence a p p r o p r i a t e l y c a l l e d
th e f lo o d - p la i n of th e stream .
The d e p o s i t i s o f n e a r l y
u n i f o r m d e p t h , d e s c e n d i n g no l o w e r t h a n t h e b o t t o m o f
t h e w a t e r c h a n n e l , and i t r e s t s upon a t o l e r a b l y even
s u r f a c e o f t h e r o c k o r o t h e r m a t e r i a l which i s c o r r a d e d
by t h e s t r e a m .
The p r o c e s s o f c a r v i n g away t h e r o c k so
a s t o p r o d u c e an even s u r f a c e , and a t t h e same t i m e c o v ­
e r i n g i t w i t h an a l l u v i a l d e p o s i t , i s t h e p r o c e s s o f
planation."
D iscussion of th e Rlaxlville Plain
C o l l i e r a nd Thom 0 9 1 7 )
f i r s t described the gravel of the F la x v ille
P l a i n i n n o r t h e r n and n o r t h e a s t e r n Montana and s a i d i t was " n o t o l d e r t h a n
Mioce ne o r y o u n g e r t h a n e a r l y P l i o c e n e " .
I t i s from a few f e e t t o 100 f e e t
t h i c k and composed o f w e l l - r o u n d e d q u a r t z i t e and a r g i l l i t e p e b b l e s from
p o r t Union f m
RocK Creek
F i g u r e 39.
V e r t i c a l p r o f i l e s a c r o s s ; A) Rock C r e e k v a l l e y and t h e a d j o i n i n g s u r f a c e I I which i s
h e r e c o v e r e d by m o r a i n e ; and B) Rock C r e e k v a l l e y and s e v e r a l n e a r b y s u r f a c e s and v a l l e y s .
See
Figure I for the lo ca tio n s of these p r o f i l e s .
F i g u r e 40 .
V e r t i c a l p r o f i l e a c r o s s Rock C r e e k v a l l e y .
See F i g u r e I f o r t h e l o c a t i o n o f t h i s p r o f i l e
78
t h e Rocky M o u n t a i n s .
Union,
I t r e s t s upon a s e r i e s o f p l a t e a u s c u t a c r o s s F o r t
Lance and Bearpaw f o r m a t i o n s and r a n g e s i n a l t i t u d e f ro m 2600 f e e t
i n t h e e a s t t o 3200 f e e t i n t h e w e s t .
C o l l i e r and Thom named t h e g r a v e l
nF l a x v i l l e " a f t e r t h e town o f F l a x v i l l e a t o p one o f t h e p l a t e a u s i n
S h e r i d a n C o u n t y , M o n ta n a .
The M i o c e n e - e a r l y P l i o c e n e age was b a s e d on f o s s i l e v i d e n c e b u t ,
q u o t e from t h e i r a r t i c l e ,
to
"None o f t h e m a t e r i a l i s s u f f i c i e n t l y good o r
c o m p l e t e t o make p o s i t i v e s p e c i f i c d e t e r m i n a t i o n s ,
no v a l u e as i n d i c a t i n g h o r i z o n ,
and i t
except in a broad way."
is therefore of
Most o f t h e f o s ­
s i l s c o l l e c t e d were o f u p p e r Miocene a g e e x c e p t f o r o n e , a P l e i s t o c e n e
came l t o o t h ( VCam elops s p . ) .
C o l l i e r and Thom d i d n o t s t a t e e x p l i c i t l y
j u s t what p o s i t i o n t h i s P l e i s t o c e n e f o s s i l o c c u p i e d i n t h e d e p o s i t , b u t i t
seems t o me t h a t u n t i l i t
is
shown o t h e r w i s e ,
it
is p o ssib le th a t the
d e p o s i t i s P l e i s t o c e n e and n o t l a t e Miocene o r e a r l y P l i o c e n e .
t h a t t h e Camelops t o o t h i s P l e i s t o c e n e ,
Assuming
and t h a t i t o c c u p i e d a p o s i t i o n
n e a r t h e t o p o f t h e d e p o s i t C a l l t h e f o s s i l s came from a " r a i l r o a d c u t " ) ,
t h e age o f t h e s u r f a c e may b e P l e i s t o c e n e ( s e e F i g u r e 4 1 ) .
C ertainly,
if
t h e f o s s i l was i n p l a c e w i t h i n t h e d e p o s i t a n d b e tw een M i o c e n e - P l i o c e n e
fo ssils,
t h e e n t i r e s e q u e n c e has t o be P l e i s t o c e n e ,
the other fo s s ils
h a v i n g bee n t r a n s p o r t e d i n .
C o l l i e r a nd Thom named t h e g r a v e l t h a t c a p s t h e C y p r e s s H i l l s i n
Canada t h e " C y p r e s s P l a i n " a nd a s s i g n e d an. O l i g o c e n e ( W h i t e R i v e r ) age t o
it.
G enerally,
th e Cypress P la in f i t s
t h e same d e s c r i p t i o n as t h e F l a x v i l l e '
P lain except t h a t i t
i s d e v e l o p e d a t h i g h e r e l e v a t i o n s and i s much more
r e s t r i c t e d in area.
The t e r m " p l a i n " ,
as in " F l a x v i l l e P l a i n " or "Cypress
79
Late P le is to c e n e gravel
i
Mid P l e i s t o c e n e g r a v e l
•°0 » 8
Early Pliocene gravel
&
r'/.v
L a t e Miocene g r a v e l
COMPOSITE SECTION
F i g u r e 4 1 . A l t h o u g h t h e f o s s i l e v i d e n c e a t any one p l a c e may i n d i c a t e an
a g e r a n g i n g from l a t e Miocene t o l a t e P l e i s t o c e n e , t h e s u r f a c e i s a c t u a l l y
la te Pleistocene.
In t h e ex am pl e a b o v e , f o s s i l s t a k e n from r o a d c u t "A"
on t h e w e s t s i d e h a l f w a y up t h e c u t would be e a r l y P l i o c e n e ; a t t h e b a s e
t h e y would be l a t e M io c e ne .
F o s s i l s t a k e n from t h e e a s t s i d e o f t h e c u t
would be e i t h e r l a t e Miocene o r l a t e P l e i s t o c e n e .
A l l t h e s e f o s s i l s might
be i n p l a c e ; some o l d o n e s m ig ht be a t t h e s u r f a c e : b u t t h e o n l y ones o f
v a lu e in d a t i n g t h e s u r f a c e a r e th o se o f l a t e P l e i s t o c e n e ,age.
The d i a g r a m abov e can be u s e d t o show t h e f a l l a c y i n C o l l i e r and Thom’ s
( 1 9 1 ; ) r e a s o n i n g in a s s i g n i n g an a g e o f M i o c e n e - P l i o c e n e t o t h e F l a x v i l l e
( u n l e s s t h e y s t a t e t h e i r e v i d e n c e more c o n c l u s i v e l y ) .
The s i t u a t i o n shown
i n t h e d i a g r a m must be q u i t e common. As a s t r e a m m ean de rs from s i d e t o
s i d e , i t w i l l n o t r e a c h b e d r o c k e ach t i m e i t meand ers o v e r an a r e a , b u t
r a t h e r i t w i l l c u t d e e p e r i n some p l a c e s t h a n o t h e r s , l e a v i n g a v e n e e r o f
f r e s h g r a v e l o f v a r y i n g d e p t h on t o p o f t h e o l d e r g r a v e l .
80
P l a i n " may be a m i s n o m e r „
do n o t p r o v e t h a t
The l e v e l summits o f t h e g r a v e l - c a p p e d p l a t e a u s
t h e f o r m e r l a n d s c a p e s were e v e r y w h e r e l e v e l .
(196 0)
suggests th a t
w h ic h ,
t o g e t h e r with th e in te r v e n in g d iv id e s ,
Howard
: t h e F l a x v i l l e g r a v e l was c o n f i n e d t o b r o a d v a l l e y s
c o n trib u te d to a r e l i e f of
hundreds o f f e e t .
A ld en (193 2) e x t e n d e d t h e o r i g i n a l F l a x v i l l e s y s t e m to o t h e r p a r t s
o f Montana and a d j a c e n t a r e a s .
S u r f a c e I I o f t h e C r a z y M ou n ta in a r e a was
i n c l u d e d by Al de n i n t h e s y s t e m o f s u r f a c e s he c a l l s F l a x v i l i e .
to Alden,
i n n o r t h e r n Montana t h e r e a r e e x t e n s i v e y o u n g e r ,
e r o s i o n a l s u r f a c e s on which g r a v e l c o v e r i s t h i n o r a b s e n t .
silts
-A ccording
lo w e r l e v e l
S tratified
and g r a v e l s a r e a l s o p r e s e n t on t h e s e s u r f a c e s i n s e v e r a l p l a c e s .
T h e s e p o s t - F l a x v i l l e s u r f a c e s a r e d a t e d by A ld e n a s p r e - W i s c o n s i n b e c a u s e
o f t h e p r e s e n c e o f W i s c o n s i n g l a c i a l m a t e r i a l on them i n c e r t a i n p l a c e s .
He a s s i g n s an a g e o f l a t e P l i o c e n e o r e a r l y P l e i s t o c e n e t o th em .
100 t o 500 f e e t dee p w e r e s u b s e q u e n t l y e r o d e d i n t h e s e b e n c h e s ,
Valleys
and Alden
f e e l s t h a t m o st o f t h i s c u t t i n g t o o k p l a c e b e f o r e t h e a d v a n c e o f t h e Wis­
consin g l a c i e r ,
which d e p o s i t e d d r i f t on u p l a n d s , b e n c h l a n d s and i n t h e
vdlleys.
Ages o f t h e S u r f a c e s
The o n l y p r e v i o u s work i n t h e a r e a s o u t h w e s t o f t h e C r a z y Mou ntai ns
aimed a t l e a r n i n g t h e a g e s o f t h e e r o s i o n a l s u r f a c e s was c a r r i e d o u t by
Al de n ( 1 9 3 2 ) .
th is area.
His work was o f a r e c o n n a i s s a n c e n a t u r e a n d n o t a c c u r a t e i n
H o r b e r g (1940) a t t e m p t e d t o c o r r e l a t e t h e t e r r a c e s o f t h e Y e l ­
lowstone V alley w ith s u rf a c e s o f th e p r e s e n t a re a ,
b u t h i s work was a p p a r ­
81
e n t l y i n f l u e n c e d by A l d e n ' s p r e v i o u s c o n c l u s i o n s .
The y o u n g e s t s u r f a c e i n t h e a r e a i s s u r f a c e IF,
I t i s an i n t r a -
W i s c o n s i n s u r f a c e b e c a u s e t h e f r e s h e s t m o r a i n e o f l a t e W i s c o n s i n ag e l i e s
on i t b u t t h e o l ^ e r W i s c o n s i n m o r a i n e d o e s n o t ( s e e F i g u r e I and a l s o t h e
discussion of surface IF),
S u r f a c e IF i s i n a p o s i t i o n su ch t h a t i f e a r l y
m o r a i n e was d e p o s i t e d on s u r f a c e ' I I I ,
s u c h m o r a i n e would a l s o hav e been
d e p o s i t e d on s u r f a c e IF i f t h e l a t t e r had e x i s t e d a t t h e t i m e .
Ib i s n o t
known wibh c e r t a i n t y t o wh ic h g l a c i a l a d v a n c e t h e e a r l y m o r a i n e b e l o n g s ,
but i t
i s pro b ab ly e a r l y W isconsin,
C o tt o n w oo d C r e e k h as c u t downward a b o u t
a h u n d r e d f e e t b e lo w t h e l e v e l o f s u r f a c e IF s i n c e W i s c o n s i n g l a c i a t i o n ;
the process continues.
Other c re e k s ap p ear to have rea c h e d base l e v e l
and a r e now i n t h e p r o c e s s o f c u t t i n g a f l o o d p l a i n .
me why t h e r e i s t h i s d i f f e r e n c e i n b e h a v i o r .
I t i s not obvious to
The t e r r a c e a l o n g t h e S h i e l d s
R i v e r ( p a g e 41) m erges w i t h s u r f a c e IF and must be o f t h e same a g e .
th e a v a i l a b l e evidence t h e r e f o r e ,
is
la te s t P leistocene,
Surface I I I ,
Figure I ) ,
All
s u b s t a n t i a t e s t h e t h e o r y t h a t s u r f a c e IF
in tra-W isco n sin in age.
th e next o ld e s t,
is w ell-developed
i n two a r e a s ( s e e
R e l a t i o n s h i p s b e tw e en t h e n o r t h e r n p a r t o f s u r f a c e I I I and
s u r f a c e IF i n d i c a t e a c o n t i n u o u s s e q u e n c e o f e v e n t s w i t h no m a j o r i n t e r ­
r u p t i o n s b e tw e en t h e c u t t i n g o f t h e s e two s u r f a c e s .
M o ra i n e o f t h e e a r l i e s t
g l a c i a l a d v a n c e l i e s on t o p o f s u r f a c e I I I i n d i c a t i n g t h a t t h e s u r f a c e i s
e it h e r e a rly or pre-W isconsin,
surfaces
Again, on ly about a hundred f e e t s e p a r a te
I I I and IF s u g g e s t i n g a r e l a t i v e l y s h o r t t i m e i n t e r v a l betw een
these surfaces.
F u r t h e r m o r e , t h e r a p i d r a t e a t which t h e n o r t h e r n p a r t o f
s u r f a c e I I I i s b e i n g d i s s e c t e d by h e a d w a rd e r o s i o n from t r i b u t a r i e s o f t h e
82
S h ie ld s River su g g ests t h a t th e s u rfa c e i s not exceedingly old;
i t would
l a s t o n l y a few t h o u s a n d y e a r s a t t h e p r e s e n t r a t e o f d i s s e c t i o n ,
(1932),
Alden
on h i s p h y s i o g r a p h i c map o f Montana, c a l l e d s u r f a c e I I I " E a r l y
P l e i s t o c e n e i n a g e , p r e - I o w a n or I l l i n o i a n
(?)
interglacial
stage".
This
c o n c l u s i o n do es n o t seem t o be w a r r a n t e d i n v i e w o f t h e p r e c e d i n g d a t a .
The n o r t h e r n and s o u t h e r n p a r t s o f s u r f a c e I I I a r e c o n s i d e r e d t o be
c o n t e m p o r a n e o u s T h e two a r e a s a r e s e p a r a t e ,
b u t a s h a s a l r e a d y been, d i s ­
c u s s e d ( p a g e 3 7 ) , r e l a t i o n s h i p s do i n d i c a t e c o n t e m p o r a n e i t y ^
Ex c e p t f o r
t h e l a c k o f g l a c i a l e v i d e n c e , r e l a t i o n s h i p s b e tw e en s u r f a c e s I I I and I I
a r e v e r y s i m i l a r t o t h o s e b e tw e e n IV and I I I ,
that is,
s e p a r a t e d by a b o u t a h u n d r e d f e e t , i n most p l a c e s ,
th e surfaces are
s l o p e s b e tw een t h e two.
s u r f a c e s a r e r e l a t i v e l y smooth, and he a d wa rd e r o s i o n from s u r f a c e I I I h a s
no-£ worked b a c k i n t o s u r f a c e I I a p p r e c i a b l y .
indicates,
G la c ia l evidence c le a r l y
ho we v e r, t h a t s u r f a c e I I i s o l d e r t h a n t h e e a r l i e s t o f t h e two
rec o g n ize d g l a c i a l advances, p robably pre-W isconsin but almost c e r t a i n l y
intra-P leistocene.
Alden mapped s u r f a c e I I a s F l a x v i l l e a n d he c a l l e d i t e a r l y P l i o c e n e ,
Horberg (1940), w h ile a c c e p t i n g A ld e n ' s i n t e r p r e t a t i o n t h a t t h e F l a x v i l l e
is
e x t e n s i v e l y d e v e l o p e d n o r t h e a s t o f Chadb or n ( he i n c o r r e c t l y l a b e l e d
"Ch ad bo rn " on h i s map, c a l l i n g i t " C l y d e P a r k " ) ,
age f o r t h e s u r f a c e ,
d isa g re e d w ith A lden's
He r e a s o n e d t h a t a l t h o u g h t h e r e i s v e r t e b r a t e f o s s i l
e v i d e n c e f o r a s s i g n i n g t h e a g e o f l a t e Miocene t o e a r l y P l i o c e n e t o t h e
F l a x v i l l e i n n o r t h e r n Montana ( I hav e q u e s t i o n e d t h i s on p a g e 7 8 ) ,
there is
a l s o v e r t e b r a t e e v i d e n c e t o s u p p o r t a l a t e Miocene t o e a r l y P l i o c e n e ag e
f o r t h e "lak e beds" in t h e Yellow stone V alley,
and i t i s d o u b t f u l w h e t h e r
83
both th e
-’l a k e b e d s " and t h e g r a v e l s c o u l d h a v e b e e n d e p o s i t e d c o n t e m p o r a n e ­
o u s l y i n t h e same r e g i o n ,
a s t h e n a t u r e o f t h e two d e p o s i t s i n d i c a t e s
c o n sid e rab ly d i f f e r e n t environm ents.
of surface II,
L i t h o l o g i c and s t r u c t u r a l r e l a t i o n s
( th e F l a x v i l l e g ra v e l o f Horberg),
to r a d i c a l l y d if f e r e n t co n d itio n s of o r ig i n .
ever,
and t h e " l a k e b e d s " p o i n t
I t seems q u i t e p o s s i b l e how- .
t o have c o n s i d e r a b l y d i f f e r e n t e n v iro n m e n ta l c o n d i t i o n s in a d j o i n i n g
a r e a s and H o r b e r g ' s ar g u m e n t may o r may n o t be v a l i d ,
although the
" F l a x v i l l e P l a i n " i s n o t known t o t r u n c a t e t h e " l a k e b e d s "
a ny w he r e w i t h i n t h e a r e a ,
i t s p r o j e c t i o n wou ld r i s e w e l l a b o v e t h e " l a k e
beds" in th e Yellow stone Valleyv
age,
He c o n t e n d e d t h a t
Because o f th e s e r e l a t i o n s h i p s ,
a younger
l a t e P l i o c e n e t o e a r l y P l e i s t o c e n e was f a v o r e d f o r s u r f a c e I I by
Horberg-,
R e l a t i o n s h i p s b e tw e e n s u r f a c e I I and I I I i n d i c a t e a c o n t i n u o u s
s e q u e n c e o f e v e n t s from t h e t i m e d r a i n a g e d i s s e c t e d s u r f a c e I I u n t i l i t
f o m re d s u r f a c e I I I ,
This f a c t ,
coupled w ith H orberg' s rea so n in g ,
strength­
ens t h e c o n te n t io n t h a t s u r f a c e I I i s e a r l y P l e i s t o c e n e in age.
S u r f a c e I , t h e o l d e s t e x t e n s i v e s u r f a c e , may b e e i t h e r I) t h e C y p r e s s
P l a i n G r a v e l o f O l i g o c e n e a g e ; 2) an i n t e r m e d i a t e s t a g e b e tw e e n t h e C y p r e s s
P l a i n and t h e F l a x v i l l e ;
3) t h e F l a x v i l l e g r a v e l ,
favor the l a s t of th ese p o s s i b i l i t i e s ,
C a n a da , t h e C y p r e s s P l a i n ,
o r 4) non e o f t h e s e ,
I
-In n o r t h e r n Montana and s o u t h e r n
d e s c r i b e d by C o l l i e r and Thom ( 1 9 17 ) i s s e p a r a t e d
v e r t i c a l l y from t h e F l a x v i l l e P l a i n by f ro m 700 t o 1500 f e e t e l e v a t i o n ,
far
more t h a n t h e v e r t i c a l s e p a r a t i o n b e tw e en s u r f a c e s I and I I i n t h e p r e s e n t
area.
A l t h o u g h t h e s e v e r t i c a l s e p a r a t i o n s m ig h t v a r y c o n s i d e r a b l y o v e r
wi de a r e a s ,
it
i s t h o u g h t t h a t s u c h an e x t r e m e amount o f e r o s i o n as i n d i c a t e d
84
f o r t h e a b o ve p l a i n s ' r e g i o n must h a v e r e q u i r e d more t i m e t h a n t h a t b e tw e en
s u r f a c e s I and I I which a r e g e o g r a p h i c a l l y and g e o l o g i c a l l y wh er e one m ig h t
expect l a r g e r e le v a tio n d if f e r e n c e s in c lo s e l y r e l a t e d s u r f a c e s ,
R e l a t i o n s h i p s b e tw e e n s u r f a c e s I and I I a r e more o b s c u r e t h a n betw een
th e o th er su rfaces because,
by s t r e a m s .
i n many p l a c e s ,
t h e two s u r f a c e s a r e s e p a r a t e d
T h e r e may h a v e b e e n an i n t e r r u p t i o n o f some m a g n i t u d e i n t h e
e r o s i o n a l c y c l e b e tw e en s u r f a c e s
I and I I wh ic h c o u l d e a s i l y b e o v e r l o o k e d .
The f a c t t h a t s u r f a c e I was o n c e much more e x t e n s i v e t h a n i t
c a te s t h a t c o n s id e r a b le e ro sio n has o c c u rre d s in c e i t s
i s now i n d i ­
form ation.
It
s h o u l d b e r e c a l l e d t h a t c h a r a c t e r i s t i c s o f s u r f a c e I im p ly a l o n g e r
exposure to w eathering co n d itio n s
Therefore,
than f o r any o f th e younger s u rfa c es..
s u r f a c e I may b e e a r l y P l e i s t o c e n e o r even o l d e r .
In t h e n o r t h e r n p a r t o f t h e C r a z y M o u n t a i n s ,
vations is q u ite g e n tle .
Loco M o u n ta i n ,
f l a t top of se v era l square m ile s .
topography at high e l e ­
r i s i n g t o 9000 f e e t h a s a n e a r l y
Al de n h a s s u g g e s t e d t h a t t h i s
surface
may d a t e b a c k t o t h e t i m e o f t h e C y p r e s s P l a i n and be o f O l i g o c e n e o r
Miocene a g e .
N e a r e r t h e a r e a c o v e r e d i n t h i s p a p e r , t h e r e a r e a few s m a l l
r e m n a n t s o f f l a t s u r f a c e s a t e l e v a t i o n s o f a b o u t 1 0 ,0 0 0 f e e t and t h e s e t o o
may c o r r e s p o n d t o an O l i g o c e n e e r o s i o n s u r f a c e ^
The amount o f e r o s i o n t h a t
o c c u r r e d b e tw e e n t h e t i m e s uc h a s u r f a c e was c u t a t t h a t h i g h e l e v a t i o n
a n d t h e t i m e s u r f a c e I was c u t i s c o n s i d e r a b l e ;
m a t e r i a l was r em ove d.
q u i te sm all,
from 2000 t o 3000 f e e t o f
There a r e s e v e r a l i n te r m e d ia t e s u r f a c e remnants,
all
a t v a r y i n g e l e v a t i o n s from 1 1 , 0 0 0 f e e t down t o t h e 7200 f o o t
maximum o f s u r f a c e I .
The l a c k o f O l i g o c e n e o r Miocene d e p o s i t s i n t h e a r e a i m m e d i a t e l y
85
s u r r o u n d i n g t h e Q r a z y M o u n ta i n s s u g g e s t s t h a t t h e a r e a was h i g h and e r o s i o n
was a c t i v e t h r o u g h o u t t h i s t i m e .
Recent d isc o v e ry in Cenozoic d e p o s it s a t
t h e m a r g i n o f t h e G a l l a t i n V a lle y o f i g n e o u s cobbles which appear t o be
d e r i v e d from t h e C r a z y Mou nta in s t o c k t o t h e n o r t h e a s t i n d i c a t e s t h a t
d r a i n a g e d u r i n g l a t e T e r t i a r y t i m e may h a v e been d i r e c t e d t o w a r d t h e s o u t h ­
w e s t a t a h i g h enough e l e v a t i o n t o t o p t h e s t r u c t u r a l s ag e a s t o f Bozeman
b e tw e e n t h e B r i d g e r Range and t h e G a l l a t i n Range (D r . W. 5 . McMannis; Mr.
P . A. G l a n c y , p e r s o n a l c o m m u n i c a t i o n ,
i n d i c a t e s t r a n s p o r t from t h e e a s t .
1962).
Im brication in th ese d ep o sits
A c c o r d i n g t o McMannis, t h e s t r u c t u r a l
c o n fig u r a tio n o f th e T e r ti a r y d e p o sits in th e southern p a r t o f th e G a lla tin
V a l l e y i n d i c a t e s t h a t t h e s t r a t a e a s t o f Bozeman p r o b a b l y a r e P l i o c e n e i n
age.
D eposition probably occurred p r i o r to a phase of P lio c e n e -P le is to c e n e
f a u l t i n g a l o n g t h e B r i d g e r Range.
C areful' study o f o t h e r p o t e n t i a l . s o u r c e s
f o r t h e i g n e o u s c o b b l e s by McMannis and G l a n c y f a i l e d t o p r o d u c e l i k e l y
p o ssib ilities.
S t u d i e s o f s e v e r a l t h i n s e c t i o n s c u t from t h e g r a v e l s i n
t h e G a l l a t i n V a l l e y and r o c k s from t h e C r a z y M o u nt a in s t e n d e d t o c o n f i r m t h e
common o r i g i n o f t h e s e r o c k s .
T e x t u r e s and m i n e r a l c o m p o s i t i o n a r e e s s e n ­
t i a l l y t h e same; p l a g i o c l a s e s o f b o t h a r e n e a r l y i d e n t i c a l .
To c a r r y t h e s e l a r g e b o u l d e r s , up t o two f e e t i n d i a m e t e r ,
g r a d i e n t most h a v e b e e n r e q u i r e d ;
a steep
i t i s p o ssib le th at the c r e s t of the
C r a z y M o u n ta i n s h a s bee n lo w e r e d 2000 t o 3000 f e e t by e r o s i o n s i n c e t h e
b o u ld e r s were t r a n s p o r t e d .
When t h e g r a v e l s were d e p o s i t e d ,
d r a i n a g e may
ha ve be e n d i r e c t e d i n t o an a n c e s t r a l Y e l l o w s t o n e R i v e r w h ic h f l o w e d w e s t ­
ward be tw e e n t h e B r i d g e r and G a l l a t i n R a n g e s .
In c o n c l u s i o n ,
c a r e f u l s t u d y o f t h e r e l a t i o n s h i p s b e tw e e n t h e
Epochi
Pleisto ­
cene
Crazy Mountains
(present paper)
1962
L a te W isconsin d r i f t
S u r f a c e IV
E a r l y W isconsitf d r i f t
Surface I I I
E ro sio n
Surface II
E ro sio n
Eastern Montana
(Alden)
1932
Yellowstone Valley
(Horberg)
1940
Wisconsin d r i f t
Late Wisconsin d r i f t
Erosion
Early Wisconsin d r i f t
Terrace No. 3
Pre-Wisconsin d r i f t
Basalt
Gravels ( "White C l if f s " )
Terrace No. 2
No. 3 Bench
Iowan-Illinoian
d r i f t (?)
No. 2 Bench
Surface I
Eastern Montana
(Howard)
1960
Sangamon
Illinoian
Yarmouth
Aftonian
loess
alluvium and slope
wash
drift
drift
Faulting and Warping (?)
No. I Bench
(F la x v ille )
Uplift
Upper Bozeman
f ’W h i t o
fm .
C H ffs")
Later glac iatio n
I n t e r g l a c i a l in te r v a l
Pre-Wisconsin stage
Superimposed drainage
Dissection of Bozeman beds
Fourth cycle of erosion
Opening of drainage
Upland surface
Pliocene
Post g l a c i a l in te r v a l
Wisconsin stage
Early glac iatio n
Terrace No. I
( F la x v ille )
Erosion
(small remnants)
Western Montana
(Atwood)
1915
F la x v ille Gravel
Local erosion at intermediate levels
Upper Bozeman beds
Aggradation in lowlands
Miocene
Oligocene
Erosion on
high flanks of
the
Crazy
Mountains
with
deposition in
nearby
areas
Faulting and Warping (?)
R im rn ad
G ravel
(Cypress Gravel)
Cypress Plain
(subsummit
peneplain)
Thirfl cycle of erosion
Closing of drainage
Second cycle of erosion
"White River formation
Early basic breccia
Lower Bozeman beds
Uplift
F i r s t cycle of erosion
Eocene
Pre-Oligocene surface
D i o r i ti c in tru s io n s
Fort Union
Fort Union
Paleocene
Mountain building
Lance
Livingston fm.
Table I.
Sentinal Butte
Tongue River
Lebo Shale
Tullock
Regional c o r r e l a t i o n chart
Pre-peneplain stage
87
v a r i o u s s u r f a c e s and g l a c i a l f e a t u r e s i n d i c a t e s t h a t t h e t h r e e most r e c e n t
s u rfa c e s a re a l l of P le is to c e n e age.
They w e r e c u t i n a c o n t i n u o u s , r e l a ­
t i v e l y r a p i d s e q u e n c e o f e v e n t s i n t e r r u p t e d by g l a c i a t i o n a t l e a s t t w i c e .
S urface I,
as shown by r e g i o n a l and s t a t i s t i c a l r e l a t i o n s h i p s ,
e it h e r l a t e Pliocene or e a rly P le is to c e n e .
f a c e I,
is older,
P r io r to th e form ation of s u r ­
g r e a t amounts o f m a t e r i a l s w er e removed from t h e m o u n t a i n s and
numerous g r a v e l c o v e r e d b e n c h e s o f r e s t r i c t e d a r e a i n d i c a t e t h a t s u r f a c e s
may ha ve e x i s t e d d u r i n g t h i s p e r i o d o f e r o s i o n .
T h i s e r o s i o n began some
tim e a f t e r th e i n t r u s i o n o f t h e igneous s to c k and i t c o n tin u e s a t th e
p rese n t tim e.
G e n e r a l C o m p a r i s o n s and C o r r e l a t i o n s
Much o f A l d e n ' s work was o f a r e c o n n a i s s a n c e n a t u r e and h i s w r i t i n g
i n d i c a t e s t h a t much o f h i s i n f o r m a t i o n i s
second-hand.
He mapped t h r e e
p r i n c i p a l s u r f a c e s t h r o u g h o u t Montana; t h e h i g h e s t e r o s i o n a l s u r f a c e ,
e q u i v a l e n t to t h e rT l a x v i l i e " he c a l l e d No. I Bench; t h e i n t e r m e d i a t e he
c a l l e d No. 2 Bench; and t h e l o w e s t he c a l l e d No, 3 Bench.
He a t t e m p t e d to
p l a c e e v e r y s u r f a c e he e n c o u n t e r e d i n t o o n e o f t h e s e t h r e e c a t e g o r i e s .
The e v i d e n c e f o r h i s c o r r e l a t i o n s
i s o f t e n va gue e x c e p t t h a t t h e h i g h e s t
s u r f a c e on t h e f l a n k s o f a m o u n t a i n r a n g e i s u s u a l l y d e s i g n a t e d No. I
Benc h.
Alden d e s c r i b e d s e v e r a l t r a c e s o f No. I Bench i n a l l p a r t s o f Mon­
t a n a ( i n c l u d i n g s u r f a c e TI o f t h e p r e s e n t a r e a ) „
He d e s c r i b e d r e m n a n ts o f
No. 2 Bench, e q u i v a l e n t t o s u r f a c e I I I o f t h e p r e s e n t a r e a .
exceptions,
With few
t h e s e s u r f a c e s a r e n o t d e s c r i b e d i n any d e t a i l b ey on d, p e r h a p s ,
a g e n e r a l d e s c r i p t i o n o f t h e g r a v e l c o v e r and a s t a t e m e n t o f t h e g r a d i e n t s .
88
Bluemle
Alden
Howard
Qal ( p r e s e n t
floodplain)
Qal
Qal
H o rb erg
Qt ( p o s t - g l a c i a l )
S -IV ( I n t r a W i s e . )
No. 3 ( p r e - W . )
Qcg ( p r e - W . )
T-3 ( p r e e a r l i e s t WJ
S - I I I (p re to
intfa-W ,)
No. 2 ( p r e - W . )
Qctg ( p f e - W . )
T-2 ( p r e Kansan o r
N e b r a sk a n )
S - I I (pre-W.)
No. I (Mio. o r
P lio J
Tfg ( P l i o J
T-I ( S - I I )
( la te P l i o . or
early P l e i s t J
Cypress P la in
(O lig.)
Trg ( O l i g . o r
M ioJ
S-I (early P le is t.)
Table 2.
The above s u r f a c e c o r r e l a t i o n t a b l e i s an a t t e m p t t o show a t a
g l a n c e t h e r e l a t i o n s h i p s b e tw e e n t h e s u r f a c e s t h a t h a v e be e n mapped i n
s e v e r a l a r e a s o f M ont an a.
On t h i s t a b l e , t h o s e s u r f a c e s wh ic h a r e o p p o s i t e
s u r f a c e s o f o t h e r w r i t e r s a r e ' c o n s i d e r e d t o be e q u i v a l e n t .
The a g e s may
n o t c h e c k b e c a u s e e a ch a g e h as b e e n a s s i g n e d by t h e w o r k e r who mapped t h e
surface.
H o r b e r g ’ s T e r r a c e No. 2 i s t h e h i g h e s t one a b ov e t h e Y e l l o w s t o n e
V alley.
I t i s r e p o r t e d t o be t h e same a g e a s t h e p o o r l y d e v e l o p e d s u r f a c e
i n s e c t i o n s 33 and 34 o f T. I N . ,
ignored th e p a rts of t h i s
tain „
R„ 10 E. o f t h e p r e s e n t a r e a ,
H o rb erg
s u r f a c e j u s t t o t h e s o u t h e a s t t o w a r d Sheep Moun­
The t e r r a c e s a r e c o v e r e d w i t h SG f e e t o r more o f g r a v e l which a l o n g
t h e Y ellow stone R iver c o n ta i n abundant v o lc a n ic m a t e r i a l s .
w er e formed- by l a t e r a l p l a n a t i o n o f t h e m a s t e r - s t r e a m ,
stone River or th e S hields R iv er.
The t e r r a c e s
e i t h e r t h e Yellow.-
T e r r a c e 'Nb. 2 i s r e g a r d e d by B o r b e r g a s
89
pre-Kansan,
p o s s i b l y pre-N ebraskan in age,
however h i s e v i d e n c e f o r a s s i g n ­
i n g su ch an a g e t o t h e t e r r a c e i s n o t c l e a r .
H o r b e r g ' s T e r r a c e No. 3 i s e x t e n s i v e l y d e v e l o p e d e a s t o f L i v i n g s t o n
s o u t h o f t h e Y e l l o w s t o n e R i v e r a t e l e v a t i o n s o f 160 t o 230 f e e t above t h e
river.
The s m a l l t e r r a c e r em n a n t i n t h e s o u t h w e s t c o r n e r o f s e c t i o n 33,
T. I N . ,
R. 10 E . ,
o f my a r e a i s c o n s i d e r e d t o be t h e same age as t h i s
terrace,
t h e two r e m n a n t s l e s s t h a n a m i l e s o u t h b e i n g i n c l u d e d i n H o r b e r g ' s
T e r r a c e No. 2 s y s t e m .
I can s e e no a p p r e c i a b l e d i f f e r e n c e betw een t h e s e
t h r e e r e m n a n t s wh ic h r e a c h a c c o r d a n t e l e v a t i o n s .
The t e r r a c e s y s te m ,
a c c o r d i n g t o H o r b e r g , b e a r s t h e same r e l a t i o n t o g l a c i a l d e p o s i t s as t h e
C i r c l e t e r r a c e o f w e s t e r n Wyoming and was c o m p l e t e d b e f o r e t h e a d v a n c e o f
t h e e a r l i e s t W i s c o n s i n ( B u l l Lake) g l a c i e r s .
T e r r a c e No. I o f H or b e rg was n o t p r e s e n t i n t h e Y e l l o w s t o n e V a l l e y .
I t i s s i m p l y t h e same s u r f a c e t h a t
I h a v e mapped a s s u r f a c e I I .
H o rb erg
accepted A lden's d e sig n a tio n of F l a x v i l l e fo r th e s u rfa c e but considered
i t t o be e i t h e r l a t e P l i o c e n e o r e a r l y P l e i s t o c e n e i n a g e .
His e v i d e n c e
i s r e v i e w e d on p a g e 82.
Howard ( 1 9 6 0 ) , w o r k i n g i n n o r t h e a s t e r n Montana, mapped s e v e r a l s u r ­
fa c e s along th e Yellowstone R iv er.
c o n s i d e r e d t o be p o s t - g l a c i a l .
Mou nta in a r e a ,
The y o u n g e s t ,
l o w e s t s u r f a c e was
I t has no o b v i o u s c o r r e l a t i v e i n t h e C r a z y
a l t h o u g h my s u r f a c e IV may be e q u i v a l e n t .
The n e x t o l d e s t
s u r f a c e i s c a p p e d by t h e C r a n e G r a v e l w h ic h Howard c a l l s p r e - w i s c o n s i n .
He maps no i n t r a - W i s c o n s i n s u r f a c e .
same a s Number 3 Bench o f A l d e n .
The C r a n e s u r f a c e seems t o be t h e
His n e x t o l d e s t i s t h e C a r t w r i g h t ,
a l s o l i s t e d as p r e - W i s c o n s i n and a p p a r e n t l y t h e same a s A l d e n ' s Number 2
Bench and H o r b e r g ' s T e r r a c e 3.
Because th e C a rtw rig h t s u r f a c e c o rresponds
90
t o No. 2 Bench o f A l d e n , I t must be t h e same as my s u r f a c e I I I .
Howard
maps t h e F l a x v i l l e G r a v e l i n n o r t h e a s t e r n Montana and a s s i g n s a P l i o c e n e
age to i t .
T h i s ag e i s b a s e d s im p l y on C o l l i e r and Thom's (191 7) f o s s i l
e v i d e n c e whi ch h a s a l r e a d y been q u e s t i o n e d i n t h i s p a p e r ( p a g e 7 8 ) .
o l d e s t s u r f a c e i n n o r t h e a s t e r n Montana i s t h e Rimroad s u r f a c e ,
The
equivalent
t o A l d e n ! s C y p r e s s P l a i n and c o n s i d e r e d by Howard t o be e i t h e r O l i g o c e n e
o r Miocene i n a g e .
To c o n f i r m t h e r e l a t i o n s h i p s d e s c r i b e d ab o v e ,
it
is im portant th at
someone c a r e f u l l y t r a c k t h e t e r r a c e s a l o n g t h e Y e l l o w s t o n e R i v e r from
s o u t h o f L i v i n g s t o n and n e a r t h e C r a z y M o u n ta i n s down t h e r i v e r t o j o i n
w i t h H ow a rd 's map a t G l e n d i v e t o s e e which s u r f a c e s a c t g a l l y c o r r e l a t e w i t h
one a n o t h e r .
Time d oe s n o t a l l o w me t o do t h i s work.
. APPENDIX A
TECHNICAL DATA
92
TECHNICAL DATA
F i e l d mapping was c a r r i e d o u t d i r e c t l y on G e o l o g i c a l S u r v e y t o p o ­
g r a p h i c maps o f t h e 7 . 5 m i n u t e s e r i e s h a v i n g a c o n t o u r i n t e r v a l o f 20 f e e t
e x c e p t 40 f e e t i n t h e m o u n t a i n s ,
T h e s e maps were o r i g i n a l l y c o n s t r u c t e d
from a e r i a l p h o t o g r a p h s by m u l t i p l e x m et ho d s i n 1951.
A e r ia l photographs
p r i n t e d to a s c a l e o f a p p ro x im a te ly 2 in c h e s to t h e m ile were used to h e lp
d i s t i n g u i s h a r e a s o f m o r a i n e n e a r t h e m o u n t a i n s b e f o r e f i e l d work ^ a s
attem pted in th e s e a re a s .
Hummocky t o p o g r a p h y o f m o r a i n e s p r o d u c e s d i s ­
t i n c t o v a t e and c i i o u l a r p a t t e r n s on a e r i a l p h o t o g r a p h s .
Much o f t h i s g eo m o r p h i c i n v e s t i g a t i o n was a c c o m p l i s h e d by c a r e f u l l y
c o m p a r i n g one t e r r a i n f e a t u r e w i t h a n o t h e r .
I n i t i a l o b s e r v a t i o n s were
made from a d i s t a n c e o f s e v e r a l m i l e s i n wh ic h o v e r a l l f e a t u n e s were
distinguished.
o f t h e wo rk .
A t e n power b i n o c u l a r was q u i t e u s e f u l d u r i n g t h i s p h a s e
More d e t a i l e d o b s e r v a t i o n s w e r e made a t key l o c a t i o n s d u r i n g
the course of the study.
O b s e r v a t i o n s from b o t h h i g h and low e l e v a t i o n s
w e r e a t t e m p t e d , b u t b e s t r e s u l t s w e r e o b t a i n e d from p o s i t i o n s o f i n t e r ­
m ediate h e i g h t .
P rofiles
Some p r o f i l e s w e r e c o n s t r u c t e d w i t h a P a u l i n a l t i m e t e r .
t a n c e s w er e d e t e r m i n e d by p a c i n g .
Because i t
Slope d i s ­
is necessary in altim eter
s u r v e y s t o e s t a b l i s h some c o n t r o l t o a v o i d e r r o r from c l i m a t i c f l u c t u a t i o n s ,
i t was n e c e s s a r y t o c l o s e e a c h t r a v e r s e on a p o i n t o f known e l e v a t i o n .
E f f o r t was made t o a v o i d p r o f i l e c o m p i l a t i o n s d u r i n g u n s e t t l e d w e a t h e r .
93
V i o l e n t s t o r m s may p r o d u c e an e r r o r e q u i v a l e n t t o 390 f e e t w i t h i n an h o u r .
The p r o f i l e s t a k e n p a r a l l e l t o t h e l e n g t h o f e ach s u r f a c e w er e c o n s t r u c t e d
g r a p h i c a l l y d i r e c t l y from t h e G e o l o g i c a l S u r v e y t o p o g r a p h i c m a p s .
Photography
The w r i t e r u s e d a R o l l e i f l e x T w i n - l e n s c a me ra and p a n c h r o m a t i c f i l m
in o b ta in in g d i s t a n t photographs f o r t h i s
was employed t o d a r k e n s k i e s .
investigation.
A yellow f i l t e r
An Agfa 35mm came ra and Eastman Kodak P a n a -
t o m i c X F i l m w e r e u s e d f o r s h o r t e r s h o t s and c l o s e - u p s .
Photography o f
l a n d - f o r m s i s b e s t a c c o m p l i s h e d a t t w i l i g h t when long shadows a c c e n t u a t e
th e form s.
STATISTICAL STUDIES
The f i r s t
two o f t h e f o l l o w i n g 44 p a g e s a r e exa mple s o f t h e methods
u s e d t o d e t e r m i n e s p h e r i c i t y and r o u n d n e s s o f s a m p l e s .
The i l l u s t r a t i o n
on t h e n e x t p a g e i s a p h o t o g r a p h i c a l l y r e d u c e d c h a r t wh ic h was u s e d f o r
v i s u a l comparison in t h e d e te r m i n a ti o n o f t h e r o u n d n e s s .
.
The g r a p h on
pa ge 95 was u s e d t o d e t e r m i n e s p h e r i c i t y a f t e r t h e b / a and c / b r a t i o s o f
e a ch r o c k w er e c a l c u l a t e d .
Pag es 96 t h r o u g h 137 c o n t a i n t h e d a t a c o l l e c t e d f o r e a c h s a m p l e .
a d i s c u s s i o n o f how e ach v a l u e was d e t e r m i n e d ,
s e e p a g e s 43 t o 45 .
i n c l u d e o b s e r v a t i o n s o f e a c h s i t e t h a t seemed p e r t i n e n t .
For
Remarks
pebble
im a g e s
f o r v is u a l
r o u n d n ess
95
C/B
I.
II.
III.
IV.
F i g u r e 43.
Disc-shaped ( o b la te -sp h e ro id )
Spherical
Bladed ( t r i a x i a l )
Rod-like (p ro la te -s p h e ro id )
D e ta iled c h a rt fo r determ ining s p h e r i c it y .
96
S a m p l e No.
I
Location:
T. 2 N . , R. 11 E . , s e c t i o n
10.
E a s t o f L i t t l e Rock C r e e k on
surface I.
Igneous rock s p h e r i c i t y :
z
0.702
Sedimentary rock s p h e r i c i t y :
O verall rock s p h e ric ity :
Roundness:
0.667
0.690
0.-404
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.69 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
66% d i o r i t e ;
F r e s h l y Br o k e n :
Remarks:
1.62 in ch es
1.67 inches
34% F o r t Union s e d i m e n t a r y r o c k s .
66%
Most o f t h e g r a v e l h e r e i s s m a l l w i t h t h e l a r g e s t c o b b l e s
observed about s ix inches a c r o s s .
This land has a t h i c k ,
h i g h c o v e r o f s a g e and i s u s e d f o r g r a z i n g .
I t was n o t e d
when t h i s s a m p l e was c o l l e c t e d t h a t t h i s a r e a m i g h t be one
of g l a c i a l outwash.
97
S a m p l e No. 2
L ocation:
T . 2 N . , R.
11 E . ,
SW 1
section
10.
North o f t h e abandoned
G i l b e r t h o m e s t e a d on s u r f a c e I .
Igneous rock s p h e r i c i t y :
0.663
Sedimentary rock s p h e r i c i t y :
O verall rock s p h e ric ity :
Roundness:
0.652
0.661
0.449
Mean p f i g n e o u s r o c k maximum d i a m e t e r s :
1.72 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
C om position:
Remarks:
1 .7 1 i n c h e s
68% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o k e n :
1.69 inches
32% F o r t Onion
66%
The l a r g e s t c o b b l e s h e r e ha v e been g a t h e r e d t o g e t h e r i n t o
piles.
The s u r f a c e w h ic h s l o p e s t o t h e s o u t h w e s t i s g r a s s -
c o v e r e d w i t h some s a g e .
Some o f t h e l a r g e r b o u l d e r s r a n g e
up t o two f e e t a c r o s s and t h e s e l a r g e r b o u l d e r s a r e q u i t e
w e ll rounded.
98
S a m p l e No,. 3
L ocation:
T,. 2 N . ,
R.
11 E „; n o r t h e d g e o f s e c t i o n
seven:
Near t h e
B i l l e r ' s M i l l Road on s u r f a c e I .
Igneous r o c k s p h e r i c i t y :
0.655
Sedimentary rock s p h e r i c i t y :
O verall rock s p h e ric ity :
R o un d ne s s :
0.766
0,670
0,388
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
I . 80 i n c h e s
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
R e m a rk s :
1*73 i n c h e s
76% d i o r i t e a nd t h e r a l i t e ;
F r e s h l y Br o k e n :
I vSO i n c h e s
24% F o r t Union
70%
Gravel cover here i s s c a rc e .
The l a r g e s t c o b b l e s o b s e r v e d were
a b o u t t h r e e i n c h e s i n maximum d i a m e t e r .
and s a g e s p a r s e .
Grass cover i s t h i c k
99
S a m p l e No. 4
Location:
T. 2 N., K„ 11 E . ,
Igneous rock s p h e r i c i t y :
0.631
Sedim entary rock s p h e r i c i t y :
O v e ra ll rock s p h e r i c i t y :
Soundness:
n o r t h w e s t c o r n e r o f s e c t i o n 18 on s u r f a c e I .
0.610
0.628
0.376
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.89 in ch e s
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f m a x i m u m , d i a m e t e r s :
Composition:
Remarks:
1.91 in ch e s
82% t h e r a l i t e and d i o r i t e ;
F r e s h l y Br o k e n :
1.95 in ch es
18% F o r t Union
82%
The r o c k c o v e r h e r e i s
sparse w ith the la r g e s t cobbles reaching
maximum d i a m e t e r s o f t h r e e i n c h e s .
Many o f t h e sa m p le s were
t h o r o u g h l y w e a t h e r e d and many had a c a l i c h e c o a t i n g .
The stir f a c e
i s c o v e r e d w i t h t h i c k g r a s s and some s a g e .
I
,
100
S a m p l e No. 5
L ocation:
T. 2 'N . , E.
11 E . ,
south p a r t o f s e c tio n
17.
N orth of L i t t l e
Rock C r e e k on s u r f a c e I .
Igneous rock s p h e r i c i t y :
0.657
Sedimentary rock s p h e r i c i t y :
O verall rock s p h e ric ity :
Roundness:
0.645
0.655
0.380
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.59 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
2.64 inches
82% t h e r a l i t e a nd d i o r i t e ;
F r e s h l y Br o k e n :
2.87 inches
18% F o r t Onion
94%
The l a r g e s t r o c k s h e r e a r e a b o u t 1% f e e t i n maximum d i a m e t e r .
These l a r g e s t rocks a r e q u i t e a n g u la r s u g g e s tin g ,
glacial t i l l .
weathered,
perhaps,
Most o f t h e s p e c i m e n s a r e q u i t e t h o r o u g h l y
and t h e i r s p h e r i c i t y can b e a c c o u n t e d f o r i n p a r t
by w e a t h e r i n g s i n c e d e p o s i t i o n .
Thi n g r a s s c o v e r s t h e s u r f a c e
101
S a m p l e No. 6
Location;
T. 2 N. , R. 11 E . ,
s e c t i o n 17.
N o r t h o f L i t t l e Bo e k C r e e k
a b o u t 100 y a r d s from s am p le n o . 5 .
Igneous rock s p h e r i c i t y :
0.657
Sedimentary rock s p h e r i c i t y ;
O verall rock s p h e ric ity :
Soundness:
0.661
0.658
0.410
Mean o f i g n e o u s r o c k maximum d i a m e t e r s ;
1.63 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
1.61 in ch e s
Composition:
and d i o r i t e ;
70% t h e r a l i t e
F r e s h l y Br o k e n :
Remarks:
1.57 inches
30% F o r t Union
72%
No l a r g e c o b b l e s a r e p r e s e n t h e r e .
no s a g e .
The s u r f a c e i s g r a s s y w i t h
102
S a m p l e No. 7
L ocation:
T. 2 N ., 8 .
11 E . ,
section
11.
A b o u t t wo m i l e s w e s t - s o u t h w e s t
o f Buck M ou n ta in on t h e u p p e r end o f s u r f a c e I . •
Igneous ro ck s p h e r i c i t y :
0.657
Sedimentary rock s p h e r i c i t y :
O verall rock s p h e r i c it y :
Soundness:
0.665
0.658
0.430
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.73 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
86% d i o r i t e ;
F r e s h l y B r ok e n:
Rem arks:
1,39 inches
1.69 inch es
14% F o r t Onion
58%
The g r a v e l c o v e r h e r e i s s p a r s e and no l a r g e c o b b l e s were
observed.
The g r a s s c o v e r i s r e l a t i v e l y t h i c k .
103
S a m p l e No. 8
L ocation:
X. 2 N . , R.
11 E . ,
Igneous rock s p h e r i c i t y :
Soundness:
II.
0.644
0.677
0.442
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.59 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
70% d i o r i t e ;
F r e s h l y Br o k e n :
Remarks:
15 on s u r f a c e
0.691
Sedimentary rock s p h e r i c i t y :
O verall rock s p h e ric ity :
ce n te r of section
1.67 inch es
1.62 inches
30% F o r t Union
64%
The s u r f a c e i s v e r y f l a t h e r e and t h e g r a v e l c o v e r i s q u i t e
sparse.
I t was n o t e d when t h i s samp le was c o l l e c t e d t h a t t h e
a r e a h e r e m ig h t c o r r e s p o n d t o s u r f a c e I t o t h e n o r t h w e s t .
104
S a m p l e No. 9
Location:
T. 2 N., R.„ 11 E .;
Igneous rock s p h e r i c i t y :
Sedimentary.
Roundness:
0.704
rock s p h e r i c i t y :
O verall s p h e ric ity :
c e n t e r o f s e c t i o n 21 on s u r f a c e I I .
0.607
0.675
0,416
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.47 in ch es
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Com position:
70% d i o r i t e ;
F r e s h l y Br o k e n :
Remarks:
1.58 inches
1 .5 1 i n c h e s
30% F o r t Union
74%
Sample was c o l l e c t e d n e a r a c a n a l - c u t .
c o b b l e s on t h e s u r f a c e h e r e .
T h e r e a r e no l a r g e
In t h e c a n a l - c u t t h e t o p f o o t o f
the p r o f i l e c o n ta in s small g r a v e l s ; beneath t h i s t h e s iz e
i n c r e a s e s s h a rp ly to about 4 in ch e s.
105
S a m p l e No.
IQ
L ocation:
I.
2 N.,
R.
H E . , n o r t h c e n t r a l p a r t o f s e c t i o n 29 a b o u t t i n e -
e i g h t h o f a m i l e s o u t h o f t h e e l e v a t i o n m a r k e r " 63 1 2 " on
Surface I I .
Igneous rock s p h e r i c i t y :
0.590
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.586
0.589
0.452
Mean b f i g n e o u s r o c k maximum d i a m e t e r s :
2.13 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Com position:
Remarks:
2.09 inches
70% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o k e n :
1.97 inches
30% F o r t Union
82%
The l a r g e s t r o c k s r a n g e up t o two f e e t a c r o s s and some o f t h e s e
are q u ite angular.
S ev eral o f th e rocks observed here,
t h e y a r e n o t w he r e t h e y w e r e d e p o s i t e d ,
c a t i n g e i t h e r d e p o s i t i o n by g l a c i e r s ,
from a g l a c i e r t o t h e n o r t h e a s t .
gathered,
hands.
although
hav e s t r i a t i o n s i n d i ­
o r , more l i k e l y ,
o ut wa sh
T h e s e l a r g e r o c k s h a v e been
b u t t h e y s u r e l y ha v e n o t been c a r r i e d f a r by human
I t wo u ld seem t h a t t h e y s h o u l d r e p r e s e n t a f a i r c r o s s -
s e c t i o n o f t h e i m m e d i a te a r e a .
Thick g rass covers th e s u rf a c e .
106
S a m p l e No.
11
L ocation:
T. 2 N.,
R.
10 E . , s e c t i o n 24 a b o v e t h e C r i s w e l l d i t c h a n d a b o u t
100 y a r d s o f f t h e r o a d , on s u r f a c e I I .
Igneous ro ck s p h e r i c i t y :
0.738
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Soundness:
0.708
0.731
0.516
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.52 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.51 i n c h e s
78% t h e r a l i t e and d i o r i t e ;
F r e s h l y Br o ke n :
1.47 in ch es
22% F o r t Union
46%
The l a r g e s t c o b b l e s h e r e a r e a b o u t s i x i n c h e s i n maximum
diam eter.
Gravels a re abundant.
c o v e r e d and t h i s
Most o f t h e s u r f a c e i s g r a s s
samp le was t a k e n from a s m a l l s a g e - c o v e r e d a r e a .
107
S a m p l e No.
12
L ocation:
T. 2 N . ,
S.
10 E . ,
Igneous rock s p h e r i c i t y :
0.647
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
s e c t i o n 25 a b o u t % m i l e s o u t h o f G o l e C r e e k .
0.591
0.624
0.458
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.70 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
C om position:
Remarks:
1.66 inches
60% d i o r i t e a nd t h e r a l i t e ;
F resh ly Broken:
1 .5 9 i n c h e s
40% F o r t Union
74%
The a b u n d a n t g r a v e l c o v e r i s m o s t l y s m a l l ( I " t o 2" ) b u t w i t h a
few l a r g e a n g u l a r b o u l d e r s a f o o t o r more i n d i a m e t e r .
The
l a r g e r b o u l d e r s a r e m o s t l y b u r i e d and on two o f them s t r i a t i o n s
were n o t i c e d .
T h i s may i n d i c a t e g l a c i a l o u t w a s h . ' The s u r f a c e
is g rass covered.
108
S a m p l e No.
13
Location:
T. 2 N.,
R.
section.
10 E . , s e c t i o n 2 7 n e a r t h e s o u t h w e s t c o r n e r o f t h e
On t h e edg e o f s u r f a c e I I n e a r t h e s l o p e t o s u r f a c e
III.
Igneous ro ck s p h e r i c i t y :
0.702
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.667
0.681
0.468
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.86 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
1.84 inches
76% t h e r a l i t e and d i o r i t e ; 24% F o r t Union
F r e s h l y Br oke n:
Remarks:
1.74 inches
64%
The l a r g e s t c o b b l e s h e r e a r e a b o u t f o u r i n c h e s i n maximum
diam eter.
Due t o t h e s p o t t y g r a v e l c o v e r which seems t o o c c u r i n
s trip s of larger m aterials,
this
samp le was c o l l e c t e d by w a l k i n g
i n a b r o a d s e m i c i r c l e s t o p p i n g a t i n t e r v a l s o f a b o u t 15 f e e t
and c o l l e c t i n g f o u r sa m p le s a t e a ch s t o p .
by s a g e and t h i n g r a s s .
The s u r f a c e i s c o v e r e d
109
S a m p l e No.
14
L ocation:
T , 2 N . , R.
10 E . ,
s e c t i o n 22 a b o u t % m i l e s o u t h e a s t o f C r i s w e l l
Ranch on s u r f a c e I I .
Igneous rock s p h e r i c i t y :
0.682
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.684
0.683
0.472
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
I .60 i n c h e s
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1. 59 i n c h e s
56% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br oken:
1.58 inches
44% F o r t Union
70%
The l a r g e s t c o b b l e s m e a s u r e a b o u t s i x i n c h e s a c r o s s and n e a r l y
all
of th ese are broken.
clover fie ld .
The s am p le was t a k e n from a c u l t i v a t e d
no
S a m p l e No.
15
L ocation:
T.
I N.,
R.
10 E . ,
n o r t h e a s t o f s a m p l e * 16 a b o u t a h a l f m i l e i n
s e c t i o n n i n e on s u r f a c e I I .
Igneous rock s p h e r i c i t y :
0.658
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.706
0.663.
0.500
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.16 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
90% d i o r i t e ;
F r e s h l y Br o k e n :
Remarks:
1.67 inches
2.13 inches
10% F o r t Union
58%
The l a r g e s t r o c k s h e r e a r e a l i t t l e o v e r a . f o o t i n d i a m e t e r .
The samp le was t a k e n from a s l i g h t l y h i g h e r s u r f a c e t h a n #16,
b u t i t was s t i l l
t h o u g h t t o be on s u r f a c e I I .
ro ck s a re s ta i n e d brown.
are abundant.
Many o f t h e
The g r a v e l s a l o n g t h i s
narrow r i d g e
Ill
S a m p l e No.
16
L ocation:
T.
IN.,
R.
IO E . ,
section
n i n e a b o u t a m i l e and a h a l f n o r t h ­
w e s t o f t h e Eyman Ranch on s u r f a c e I I i
Igneous ro ck s p h e r i c i t y :
0.660
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.616
0.642
0.512
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.91 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
58% d i o r i t e ;
F resh ly Broken:
Remarks:
1 .8 4 i n c h e s
1.88 inches
42% F o r t Union
74%
The g r a v e l c o v e r h e r e i s a b u n d a n t and i t a p p e a r s t o b e a b ou t
15 f e e t t h i c k .
Thos e g r a v e l s on t o p a r e much s m a l l e r t h a n t h o s e
on t h e s l o p e s .
Many f r a g m e n t s l i e a b o u t and commonly t h e l a r g e r
p i e c e from whi ch t h e y ha v e b e e n c h i p p e d i s t h e r e .
were r e j e c t e d in t h e sam pling.
The l a r g e s t c o b b l e s seen (on
to p ) a r e about e i g h t in c h e s in d ia m e te r .
a r e w a t e r w o r n and w e l l r o u n d e d .
Obvious c h i p s
These l a r g e cobbles
112
S a m p l e No.
17
L ocation:
T. 2 N.,
S.
10 E . ,
C r e e k Road.
N o r t h o f Rock C r e e k on s u r f a c e I I I ,
Igneous rock s p h e r i c i t y :
0.654
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
n e a r t h e c e n t e r o f _s e c t i o n 24 a l o n g Ro ck
0.643
0.651
0.506
Mean o f i g n e o u s r o c k -.maximum d i a m e t e r s :
2.41 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m f e t e rs :
Composition:
72% d i o r i t e ;
F r e s h l y Br o k e n :
Remarks:
1 .5 5 i n c h e s
2.17 inches
28% F o r t Union
50%
L arg est rocks a r e about a fo o t a c r o s s .
rocks a re w ell rounded.
Nearly a l l of th e la r g e
S u r f a c e i s c o v e r e d by s a g e and g r a s s .
113
S a m p l e No.
18
L ocation:
T. 2 N.,
R.
10 E . ,
n o rth w e st c o r n e r o f s e c tio n 27 about 3 /8
m i l e s o u t h w e s t o f C r i s w e l l Ranch on s u r f a c e I I I n o r t h o f RocIc
Creek.
Igneous rock s p h e r i c i t y :
0.666
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.631
0.653
0.536
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.06 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Com position:
Remarks:
2.08 inches
78% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o k e n :
2.15 inches
24% F o r t Union
54%
The g r a v e l c o v e r h e r e i s n o t a b u n d a n t ,
(5-8 inches) cobbles a re p r e s e n t.
sample,
i t appears t h a t t h i s
From t h e l o c a t i o n o f t h e
s u r f a c e i s t h e same as s u r f a c e I I I
acro ss th e creek to th e southw est.
surface.
but se v e ra l r a t h e r larg e
Sage and g r a s s c o v e r t h e
)
114
S a m p l e No * 19
Location;
Ti 2 N., B. IO E . , c e n t e r o f s e c t i o n 21 n o r t h o f t h e r o a d on
surface I I I .
O n e - h a l f m i l e w e s t - n o r t h w e s t o f C r i s w e l l Ranch.
Igneous rock s p h e r i c i t y :
0.697
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.670
0.691
0.584
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.87 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
.1.84 i n c h e s
76% d i o r i t e and t h e r a l i t e ;
F re sh ly Broken:
1.73 inches
24% F o r t Union
28%
L arg est cobbles a re about s ix inches in d iam e te r.
cover th e surface.
Sag e and g r a s s
115
Sample No, .20
^
/ t ■- I* • •
Location:
—- '
.
. —
.
T. 2 N,-, R. 10 E . , w e s t edg e o f s e c t i o n 28.
.4.
West-northwest of
P l e a s a n t View Sc h o o l % m i l e .
Igneous rock s p h e r i c i t y :
0,700
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Soundness:
0.680
0,695
0,474
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.83 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.81 in ch e s
72% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o k e n :
1.75 inches
28% F o r t Union
58%
The l a r g e s t c o b b l e s h e r e a r e a b o u t s i x t o n i n e i n c h e s a c r o s s .
The g r a v e l c o v e r i s
the s u rfa c e .
abundant.
Some s a g e b u t m o s t l y g r a s s c o v e r
116
S a m p l e Nb. 21
Location:
T. 2 N.> S. IO E . ,
s o u t h edg e o f s e c t i o n 30.
E a s t o f Rock
C r e e k a b o u t % m i l e a l o n g Rock C r e e k Road on s u r f a c e I I I ,
Igneous ro ck s p h e r i c i t y :
0.626
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.686
0.650
0.504
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2 .0 3 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
R e m a rk s :
1.96 inches
62% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br oke n:
1.83 inches
38% F o r t Union
70%
Many o f t h e r o c k s h e r e h a v e be e n b r o k en due t o t h e f a c t t h a t
t h e a r e a has be e n c u l t i v a t e d i n t h e p a s t .
covered with g r a s s .
A
The s u r f a c e i s
117
S a m p l e No. 22
Location:
T .3
N . , . R. IO E i , s o u t h o f I b e x Mo un tai n on s u r f a c e I I I i n
s e c t i o n 35.
Igneous rock s p h e r i c i t y :
0.648
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
0.706
0.667
R oundness:: 0.481
Mean o f i g n e o u s ,rock.maximum d i a m e t e r s : ■. 4..87'. i n c h e s
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
R e m a rk s :
4.67 inches.
68% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o k e n :
4.22 inches
32% F o r t Union
46%
The l a r g e s t b o u l d e r s s e e n i n t h i s a r e a m e a s u r e a b o u t two f e e t
in d iam e te r.
B e c a u s e t h e r e a r e o n l y a few r o c k s on t h e s u r f a c e ,
t h e s am pl e a r e a was e x t e n d e d t o a b o u t a s q u a r e b l o c k .
The
r o l l i n g t o p o g r a p h y h e r e s u g g e s t s t h a t t h i s may be an a r e a o f
o ld moraine.
To t h e s o u t h e a s t t h e s u r f a p e i s
flatter.
118
S a m p l e No. 2 3
L ocation:
£.
2 IN., S .
IO S . ,
n o r t h h a l f o f s e c t i o n 4 a lo n g t h e edge o f
surface I I I .
Igneous ro ck s p h e r i c i t y :
No d a t a
Sedimentary rock s p h e r i c i t y :
O v e ra ll rock s p h e r i c i t y :
Soundness:
No d a t a
0.616
0.568
Mean o f i g n e o u s , r o c k maximum d i a m e t e r s :
No d a t a
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
4.67 inches
90% t h e r a l i t e and d i o r i t e ;
F re sh ly Broken:
No d a t a
10% F o r t Union
38%
The l a r g e s t b o u l d e r s i n t h i s a r e a m e a s u r e a b o u t -two f e e t i n
diamfetef.
The samp le was c o l l e c t e d by w a l k i n g i n a s t r a i g h t
l i n e and s t o p p i n g e v e r y f i v e p a c e s t o s e l e c t a s p e c i m e n .
su rfa c e is g rass covered.
The
119
S a m p l e No. 24
Location:
T. "3 N , , R. 9 E . , s o u t h edge o f s e c t i o n 36 a b o u t two m i l e s s o u t h
o f t h e D e A tl e y Ranch on s u r f a c e I I I .
Igneous rock s p h e r i c i t y :
0.675
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.650
0.664
0.554
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.48 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.52 inches
60% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o k e n :
1.57 i n c h e s
40% F o r t Union
54%
The l a r g e s t c o b b l e s h e r e a r e a b o u t f i v e i n c h e s i n d i a m e t e r .
L a r g e r p a r t i c l e s a p p e a r t o be b e t t e r r o u n d e d t h a n t h e s m a l l .
The s u r f a c e i s s a g e - c o v e r e d .
120
S a m p l e No. 2 5
L ocation:
T, 2 N . , R, 9 E . ,
section
12 a b o u t 5 0 f e e t
southeast of th e
n o r t h e r n m o s t c o r n e r i n t h e r o a d on s u r f a c e I I I .
Igneous rock s p h e r i c i t y :
0.663
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.607
0.649
0.514
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.85 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Com position:
Remarks:
1.77 inches
76% t h e r a l i t e and d i o r i t e ;
F r e s h l y Br o ke n :
1 .5 2 i n c h e s
24% F o r t Union
50%
Many o f t h e sp e c i m e n s h e r e ha v e a c a l i c h e c o v e r i n g .
c o b b l e s r a n g e up t o a b o u t s i x i n c h e s a c r o s s .
the surface.
The l a r g e r
High s a g e c o v e r s
121
S a m p l e No. 26
Location:
T. 3 N.., S. 9 E . ,
n o r t h edg e o f s e c t i o n 36 a b o u t one m i l e s o u t h
o f t h e DeA tle y Ranch.
Igneous ro ck s p h e r i c i t y :
0.664
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
N o rt h o f I n d i a n C r e e k on s u r f a c e I I I .
0.617
0.649
0.512
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1 .6 1 i n c h e s
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.63 inches
68% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o ke n :
1,65 inches
32% F o r t Union
58%
The l a r g e s t c o b b l e s s e e n h e r e a r e a b o u t f o u r i n c h e s i n maximum
d i a m e t e r and b r o k e n f r a g m e n t s a r e common.
ha v e a c a l i c h e c o a t i n g .
Most o f t h e sam pl es
The s p a r s e n e s s o f r o c k s f o r c e d me t o
c o l l e c t most s p e c i m e n s from a r o u n d r a b b i t b u r r o w s .
122
S a m p l e No. 27
L ocation:
T . 2 N . , R. 9 E . , n o r t h e d g e o f s e c t i o n t h r e e .
On t o p o f an
i s o l a t e d h i l l n o r t h o f I n d i a n C r e e k on s u r f a c e I I I .
Igneous rock s p h e r i c i t y :
0.614
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Soundness:
0.587
0.604
0.502
Mean of. i g n e o u s r o c k maximum d i a m e t e r s ;
1.58 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f m a x i m u n v ' d ia m e t e rs :
Composition:
Remarks:
1.75 inches
62% d i o r i t e and t h e r a l i t e ;
F resh ly Broken:
2 . 0 4 . inches
38% F o r t Union
60%
G ravel i s abundant h e re .
At t h e s l o p e - b r e a k ,
cobbles in c r e a s e s g r e a t l y .
the s iz e o f the
T h i s i s b e c a u s e e r o s i o n i s more
r a p i d on t h e s l o p e s t h a n on t h e f l a t a r e a s ,
and t h i s e r o s i o n i s
d i f f e r e n t i a l i n t h a t i t moves away t h e f i n e s w h i l e l e a v i n g t h e
l a r g e r g rav e ls behind.
Thus , t h e r o c k s on t h e s l o p e a r e " s o r t e d "
and n o t a t r u e i n d i c a t i o n o f what was o r i g i n a l l y d e p o s i t e d .
th e slopes,
broken.
also,
On
t h e r o u n d n e s s i s g r e a t e r and l e s s p i e c e s a r e
123
S a m p l e No. 2 8
Location;
T. 2 N . , R, 9 E . ,
southwest c o rn e r o f s e c tio n
14.
About two
m i l e s n o r t h e a s t o f C l y d e P a r k on t h e edge o f s u r f a c e I I I .
Igneous rock s p h e r i c i t y :
0.655
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.655
0.655
O1584
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.73 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
C om position:
Remarks:
1.65 inches
68% d i o r i t e and t h e r a l i t e ;
F re sh ly Broken:
1.50 inches
32% F o r t Onion
58%
Many o f t h e s p e c i m e n s a r e s t a i n e d brown.
Sample was c o l l e c t e d
n e a r t h e canyo n edg e b u t a b o v e t h e p o i n t t o wh ic h he ad wa rd
e r o s i o n has p r o g r e s s e d .
grass,
both in abundance.
The s u r f a c e i s c o v e r e d w i t h s a g e and
124
S a m p l e No. 29
L ocation:
T.
2 N . , R. 9 E . ,
n o r t h e a s t c o r n e r o f s e c tio n 27.
N ortheast of
tfie C l y d e P a r k c e m e t a r y on s u r f a c e I I I .
Igneous rock s p h e r i c i t y :
0.673
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.610
0.655
0.570
Mean o f . i g e n o u s r o c k maximum d i a m e t e r s :
1.46 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.44 inches
58% d i o r i t e and t h e r a l i t e ;
F resh ly Broken:
1.42 inches
42% F o r t Union
62%
The l a r g e s t c o b b l e s se en h e r e w e r e f o u r t o f i v e i n c h e s a c r o s s and
o f t a b l u l a r shape.
The s am p le was t a k e n v e r y n e a r t h e s o u t h e a s t e r n
most p a r t o f s u r f a c e I I I .
125
S a m p l e No. 30
L ocation:
T. 2 N.,
R.
10 E 1, n o r t h w e s t c o r n e r o f s e c t i o n
two.
Near t h e
c e n t e r o f s u r f a c e IV.
Igneous rock s p h e r i c i t y :
No d a t a
Sedimentary ro ck s p h e r i c i t y :
O verall s p h e ric ity :
Soundness:
No d ata'
0.634
0.496
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
No d a t a
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
R e m a rk s :
6.58 inches
85% d i o r i t e and t h e r a l i t e ;
F resh ly Broken:
No d a t a
15% F o r t Onion
44%
The s am pl e was c o l l e c t e d o v e r a r a t h e r l a r g e a r e a b e c a u s e t h e
g r a v e ls a re not abundant in th e a re a .
p r e s e n t ho wever,
Those g r a v e l s t h a t a r e
a r e q u i t e l a r g e and t h e l a r g e s t r o c k s t e n d t o
be f r e s h l y b o r k e n .
T h i s may be an a r e a o f g l a c i a l o u t w a s h .
The r e m a r k s f o r samp le No. 22 a r e a p p l i c a b l e h e r e a l s o .
126
S a m p l e No. 31
L ocation:
T. 2 N . , R.
IV.
IO E . ,
0.578
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
0.629
0.593
0.498
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.58 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
C om position:
1 .6 5 i n c h e s
2.29 inches
68% d i o r i t e and t h e r a l i t e ;
F re sh ly Broken:
Remarks:
s e v e n on s u r f a c e
About 100 y a r d s w e s t o f t h e r o a d s o u t h o f t h e M i l l e r R a n c h „
Igneous ro ck s p h e r i c i t y :
Soundness:
n o rth c e n tra l part of section
32% F o r t Union
48%
Many o f t h e s p e c i m e n s hav e a c o v e r i n g o f c a l i c h e .
The l a r g e r
c o b b l e s a r e commonly wh ol e w h e r e a s t h e s m a l l e r o n e s t e n d t o be
f r e s h ly broken.
127
S a m p l e No. 32
L ocation:
T . 2 N . , R. 9 E . ,
ce n te r o f section
14 n o r t h o f C o t t o n w o o d C r e e k
on t h e s u r f a c e b e l o w I I I .
Igneous rock s p h e r i c i t y :
0.705
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.687
0.702
0.562
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.76 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Com position:
Remarks:
1 .8 1 i n c h e s
76% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o ke n ;
1.98 inches
24% F o r t Union
40%
The l a r g e s t r o c k s are a b o u t a f o o t i n d i a m e t e r .
rocks a r e a l l w e ll rounded.
s a g e and g r a s s c o v e r .
The s u r f a c e i s
These l a r g e s t
covered w ith a th ic k
128
S a m p l e No. 33
L ocation:
T. 2 N . , R 1 9 E . ,
so utheastern % of section
14,
south o f
C ot to n w o o d C r e e k on s u r f a c e IV.
Igneous rock s p h e r i c i t y :
0.667
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.703
0.676
0,588
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.45 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean oflmaximum d i a m e t e r s :
Com position:
2.31 inches
76% d i o r i t e and t h e r a l i t e ; 24% F o r t Union
F r e s h l y Br o ke n ;
Remarks:
1.92 inches
32%
B o u l d e r s h e r e r a n g e up t o 18 i n c h e s a c r o s s .
Most o f t h e sa mples
w e r e p a r t i a l l y b u r i e d and many s p e c i m e n s had a c o v e r i n g o f
caliche.
The s u r f a c e i s c o v e r e d w i t h s a g e .
129
S a m p l e No. 34
L ocation:
I.
2 N . , R. 9 E . ,
m id d le o f s e c t i o n 27,
s o u th e a s t o f road about
400 y a r d s on s u r f a c e IV.
Igneous rock s p h e r i c i t y :
0.711
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.720
0.714
0.678
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.05 inches
Mean, o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.95 inch es
62% d i o r i t e and t h e r a l i t e ;
F re sh ly Broken:
1.77 inches
38% F o r t Union
26%
Many o f t h e s a m p l e s w er e c o v e r e d w i t h a l a y e r o f - c a l i c h e .
s u rfa c e i s covered w ith sage.
The
130
S a m p l e No. 35
L ocation:
T . 2 N . , R. 9 E ff
100 y a r d s
f r o m 34 on t h e l o w e s t o f t h r e e
surfaces.
Igneous ro ck s p h e r i c i t y :
0.696
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Boundness:
0.655
0.677
0.530
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.16 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Com position:
Remarks:
2.14 inches
54% d i p r i t e and t h e r a l i t e ;
F r e s h l y Br oke n:
2.11 inches
46% F o r t Union
36%
Many o f t h e l a r g e r c o b b l e s a r e b r o k e n .
The l a r g e s t r o c k s r a n g e
up t o
sage co v ered .
10 i n c h e s a c r o s s .
Th e s u r f a c e i s
131
S a m p l e No. 36
Location:
T. 2 N . , R,- 9 E . ,
s e c t i o n 26 on RqcIt C r e e k Road a b o u t one m i l e
e a s t o f C l y d e P a r k on t h e t h i r d i n t e r m e d i a t e s u r f a c e .
Near t h e
e dg e o f t h e s u r f a c e .
Igneous r o c k s p h e r i c i t y :
0.633
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0.645
0.635
0.510
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.97 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
C om position:
1,83 inches
44% d i o r i t e ; 56% F o r t Union
F r e s h l y Br o k e n :
Remarks:
1.73 inches
62%
The l a r g e s t c o b b l e s a r e a b o u t s i x i n c h e s i n d i a m e t e r .
samples were c a l i c h e c o v e re d .
Many
132
S a m p l e No. 37
L ocation:
T . 2 N.-, H.
IO E „ ,
n o rth east corner section
18 on t o p o f C h o s e
H ill.
Igneous rock s p h e r i c i t y :
0.623
Sedimentary rock s p h e r i c i t y ;
O verall s p h e ric ity :
Roundness:
0.543
0.612
0.446
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.66 in ch es
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.75 inches
62% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o k e n :
1.89 inches
38% F o r t Union
56%
The l a r g e s t c o b b l e s e e n was j u s t o v e r a f o o t i n d i a m e t e r .
m aterial is
s m a l l and f r a g m e n t a l .
sparse g rass.
The s u r f a c e i s b a r e w i t h
Most
133
S a m p l e No. 38
L ocation:
T.
IN.,
R.
11 E . ,
Igneous rock s p h e r i c i t y :
0.645
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
to p o f Choice-to-Death B u tte
0.648
0.646
0.510
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1.86 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
1.87 inch es
84% d i o r i t e and t h e r a l i t e ;
F re sh ly Broken:
1.94 inches
16% F o r t Union
52%
L a r g e s t specimens a r e about one f o o t a c r o s s .
The f l a t s u r f a c e
i s g r a s s c o v e r e d b u t t r e e s grow a r o u n d t h e e d g e s a t t h e s l o p e
breaks.
134
S a m p l e No. 39
L ocation:
T.
I N . , E.
10 E . ,
c e n t e r o f s e c t i o n 25 ab o u t % m i l e from t h e
o ld F a l l s School s i t e .
Igneous rock s p h e r i c i t y :
0.688
Sedimentary ro ck s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
0*695
0.689
0.446
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
2.04 inches
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
2.03 inches
78% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o ke n :
1.98 inches
20% F o r t U n i o n ; 2% c a l c i t e
82%
The l a r g e s t r o c k s a r e a b o u t 4 i n c h e s i n d i a m e t e r .
T h i s sample
i s b i a s e d i n t h a t t h e a n g u l a r s c r a p s o f F o r t Union l y i n g a ro u n d
wh ic h h a v e been b r o k e n from t h e a d j a c e n t b e d r o c k w er e r e j e c t e d .
The a r e a i s one o f r o l l i n g t o p o g r a p h y c o n t r o l l e d by t h e s t r u c t u r e .
Many o f t h e r o c k s a r e c a l i c h e c o v e r e d .
135
S a m p l e No. 40
L ocation:
T.
I S.,
E.
10 E . ,
th e h i l l about
Igneous rock s p h e r i c i t y :
Roundness:
%
o f
section th re e .
On t o p o f
m i l e . n o r t h o f B o h le e n Ranch.
0.706
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
southw estern
0.700
0.704
0.568
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
1 .8 1 i n c h e s
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s ;
Mean o f maximum d i a m e t e r s :
Com position:
1.94 inches
1.85 inches
68% d i o r i t e and t h e r a l i t e ;
22% F o r t U n i o n ; 6% q u a r t z i t e ;
2% d o l o m i t e ; 2% o t h e r i g n e o u s r o c k s
F re sh ly Broke^:
Remarks:
54%
The l a r g e s t c o b b l e s a r e a b o u t e i g h t i n c h e s i n d i a m e t e r .
The
d i f f e r e n t c h a r a c t e r o f t h e g r a v e l s on t h i s h i l l a l o n g w i t h t h e
position of the h i ll
seem t o i n d i c a t e t h a t i t i s a t e r r a c e o f
e i t h e r the S h ie ld s or Yellowstone R iv e r.
stained.
Many o f t h e r o c k s a r e
136
S a m p l e No. 41
L ocation;
T. 2 N . , R.
IO E . , c e n t e r o f s e c t i o n two on C o t t o n w o o d C r e e k .
Igneous ro ck s p h e r i c i t y ;
No d a t a
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
No d a t a
0.622
0.666
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
No d a t a
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
5 .29 inches
94% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o ke n :
No d a t a
6% F o r t Onion
12%
The l a r g e s t b o u l d e r i n t h e i m m e d i a t e a r e a i s a b o u t t h r e e f e e t in
d i a m e t e r and i t
i s F o r t U n io n.
The p u r p o s e o f t h i s
and t h e
f o l l o w i n g s a m p l e i s t o l e a r n how s p h e r i c i t y , r o u n d n e s s ,
behave under p r e s e n t c o n d it io n s o f d e p o s it io n ,
t h e p re s e n t c o n d itio n s to th o se in th e p a s t.
etc.,
and t o compare
137
S a m p l e No. 42
L ocation:
I,
2 N.,
R.
10 E . ,
eastern h a lf of section
s e v e n on C o t t o n w o o d
Creek.
Igneous rock s p h e r i c i t y :
0.686
Sedimentary rock s p h e r i c i t y :
O verall s p h e ric ity :
Roundness:
.0.644
0.673
0.724
Mean o f i g n e o u s r o c k maximum d i a m e t e r s :
3.52 inches.
Mean o f s e d i m e n t a r y r o c k maximum d i a m e t e r s :
Mean o f maximum d i a m e t e r s :
Composition:
Remarks:
3.45 inches
68% d i o r i t e and t h e r a l i t e ;
F r e s h l y Br o ke n :
3.27 inches
32% F o r t Union
4%
The l a r g e s t b o u l d e r s e e n i n t h e i m m e d i a t e a r e a was a b o u t one and
one h a l f f e e t i n d i a m e t e r .
APPENDIX B
SUMMARY OF THEORIES ADVANCED TO EXPLAIN THE FORMATION
OF PEDIMENTS
139
SUMMARY OF THEORIES ADVANCED TO EXPLAIN THE ORIGIN OF PEDIMENTS
Introduction
S i n c e l a t e i n t h e l a s t c e n t u r y , when p e d i m e n t s wer e f i r s t r e c o g n i z e d
and d e s c r i b e d ,
(G ilbert,
1877; McGee,
t h e s e f e a t u r e s has t a k e n p l a c e .
1897),
a f a i r l y co n tinuous study of
F o r the p a s t s e v e r a l y e a r s , however,
l i t t l e h a s bee n w r i t t e n on t h e s u b j e c t even th o u g h t h e p r o b l e m s c a n n o t be
,
r e g a r d e d a s h a v i n g been s e t t l e d .
The f o l l o w i n g d e f i n i t i o n o f a p e d i m e n t , t a k e n from t h e w r i t i n g s o f
D ou gl a s J o h ns o n (1932) m ig h t s a t i s f y a m a j o r i t y o f t h e s t u d e n t s o f p e d i ­
ments;
"A p e d i m e n t i s a smooth r o c k p l a i n which forms t h e h i g h e r p o r t i o n
o f t h e f a r - s p r e a d i n g lo w l an d p l a i n wh ic h i n c l i n e s away from t h e l a r g e r
m o u n t a i n m a s s e s ; a zon e s e v e r a l m i l e s b r o a d ,
i n which b e d r o c k i s a b u n d a n t l y
e x p o s e d a t t h e s u r f a c e and t h e a l l u v i u m i s r e s t r i c t e d t o a t h i n and
discontinuous v e n e e r."
S e v e r a l w r i t e r s b e s i d e s Joh n so n ha v e made m a j o r
c o n t r i b u t i o n s t o u n d e r s t a n d i n g how p e d i m e n t s havfe form ed , among them
Dutton (1882), P aige (1912),
Lawson ( 1 9 1 5 ) ,
Blackwelder (1929),
( 1 9 3 2 ) , F i e l d ( 1 9 3 5 ) , R i c h ( 1 9 3 5 ) , Mackin ( 1 9 3 7 ) , Dav is ( 193 0,
193 8) , JShape ( 1 9 4 0 ) ,
list
Howard ( 1 9 4 2 ) , C h i l d s ( 1 9 4 8 ) ,
i s n o t c o m p l e t e by any means b u t i t
and
Bryan
1933,
King (1953).
is thought th a t i t
1936,
This
i n c l u d e s most
o f t h e i m p o r t a n t v i e w p o i n t s on t h e s u b j e c t .
The o b j e c t h e r e i s n o t to p r e s e n t an e x h a u s t i v e e x p a t i a t i o n on t h e
l i t e r a t u r e t h a t has bee n w r i t t e n a b o u t p e d i m e n t s , b u t r a t h e r t o d i s c u s s
b r i e f l y some o f t h e m a j o r i d e a s t h a t h a v e been p r e s e n t e d and t o g i v e
an e v a l u a t i o n w i t h s p e c i a l e m p h a s is on t h e a r e a s o u t h w e s t o f t h e C r a z y
Mountains.
140
M a jo r I d e a s About t h e O r i g i n o f Pediments
An e a r l y t h e o r y a d v a n c e d by su ch w r i t e r s as P a i g e C1912) and Lawson
( 1 915 ) a d v o c a t e d t h a t r o c k t e r r a c e s
a re r e s u r r e c t e d s u r f a c e s due to th e
s t r i p p i n g o f a l l u v i u m w hi ch was l a i n on them as t h e y f o r m e d .
Paige
e n v i s i o n e d a r o c k - c u t b e n c h p r o c e e d i n g m o u n ta in w a rd and c l o s e l y f o l l o w e d by a
g r a v e l c o v e r wh ic h c o v e r s t h e lo we r p a r t o f t h e be nch a s more bench i s
formed.
The r o c k - c u t p a r t o f t h e s u r f a c e i s formed by i n t e r s t r e a m e r o s i o n ,
l a t e r a l c u t t i n g a t th e edges o f t h e a c cu m u latin g fan s,
b u r ia l of low -lying a r e a s .
process,
Since t h e g ra v e l cover is r i s i n g during t h i s
a r i s e in th e l o c a l base le v e l i s im p lied .
le v e l ceased to r i s e ,
t h e g r a v e l c o v e r i s removed,
rockycut su rface.b eh in d .
and p r o g r e s s i v e
Paige f e l t th a t
is
when b a s e
leaving th e underlying
sheet-flood erosion,
by McGee as t h e f o r m a t i v e a g e n t f o r p e d i m e n t s ,
c u t p l a i n and n o t a c a u s e o f i t .
F inally,
advocated
the r e s u l t o f th e rock-
Lawson e m p h a s i z e d w e a t h e r i n g and r i l l
wash as b e i n g more i m p o r t a n t t h a n l a t e r a l p l a n a t i o n .
The s i t u a t i o n s o u t ­
l i n e d by P a i g e and. Lawson w er e l i m i t e d t o a r i d and s e m i - a r i d r e g i o n s .
Ross F i e l d (193 5) s a i d t h a t t h e p e d i m e n t , which he c a l l e d a r o c k plain,
i s t h e work o f g r a d e d s t r e a m s i s s u i n g from t h e c a n y o n s and r a v i n e s „
The p e d i m e n t i s most e x t e n s i v e a l o n g t h e m a j o r s t r e a m s and i s i n a d j u s t ­
ment w i t h t h e c a r r y i n g power and l o a d o f t h o s e s t r e a m s .
wa rd ,
according to F ie ld ,
by t h e p r o g r e s s i v e s h i f t o f t h e g r a d e d p a r t up­
s t r e a m as t h e p r o f i l e o f e q u i l i b r i u m i s f l a t t e n e d .
graded in i t s
I t grows m o u n t a i n -
The s t r e a m has been
lo we r r e a c h e s f o r a l o n g e r t i m e and h e n c e has been a b l e t o
widen i t s
v a l l e y more e x t e n s i v e l y t h e r e .
Each f l o o d p l a i n becomes n a r r o w e r
upstream;
h e n c e t h e ’-’b a y s " i n t h e m o u n t a i n f r o n t .
141
F i e l d ' s c o n s i d e r a t i o n o f t h e p a r t o f t h e r u n o f f a b ov e t h e p e d im e n t
seem p e r t i n e n t .
He m a i n t a i n s t h a t t h e s h a r p b r e a k i n s l o p e b e tw een t h e
lo we r s u r f a c e and t h a t o f t h e m o u n ta in i s e x p l a i n e d by c o n s i d e r i n g t h e
r u n o f f , w h ic h i s u n c o n c e n t r a t e d on t h e s t e e p e r e l o p e s b u t c o n c e n t r a t e d on
t h e l ow e r s l o p e s .
Where t h e h i l l s i d e s c a r v e d by r i l l s
t h e f l o o d p l a i n s c a r v e d by t h e m a j o r s t r e a m s ,
break in p r o f i l e .
tain front
Thus ,
o r s h e e t w a s h meet
t h e r e must be an a n g u l a r
t h i s a n g u l a r b r e a k i n t h e p r o f i l e a l o n g a moun­
i s due t o a d i f f e r e n c e
in t h e power o f t h e a g e n c i e s d e t e r m i n i n g
i t and c a n n o t b e due t o such p r o c e s s e s a s r i l l s
f l o w i n g down t h e m o u n ta in
s l o p e s and i m m e d i a t e l y c h a n g i n g t h e i r a b i l i t y t o c a r r y d e t r i t u s on t h e
g e n t l e r slo p e o f th e pediment.
G enerally,
t h e w r i t e r s abov e f e l t t h a t t h e p r o c e s s e s t h a t
lead to
p e d i m e n t s a r e most e f f e c t i v e i n a r i d o r s e r a i - a r i d r e g i o n s w he re t h e s t r e a m s
even t h o u g h t h e y f l o w i n t e r m i t t e n t l y ,
a r e powerful e ro s iv e agents because
t h e y f l o w on s t e e p g r a d i e n t s and w h i l e i n f l o o d h a v e an a b u n d a n t volume o f
w a t e r and a m o d e r a t e y e t a d e q u a t e q u a n t i t y o f d e b r i s t o u s e a s c u t t i n g
tools.
The p r o c e s s e s wh ic h co mbined t o form p e d i m e n t s we re t h e combined
a c t i o n o f l a t e r a l w a n d e r i n g and l a t e r a l p l a n a t i o n , r i l l
e r o s i o n and w e a t h e r
ing.
A s e c o n d t h e o r y c a l l e d upon t o e x p l a i n p e d i e m t s i s b a s e d i n p a r t
on McGee' s s h e e t w a s h t h e o r y .
D a v i s (1 930 ,
p ro c e s s o f "backwearing" (w eath erin g ,
1933,
1936,
1938) f a v o r e d t h e
r a i n wash, and r i l l wash) a i d e d by
"do wn w ear ing " ( d o w n c u t t i n g by s t r e a m s ) o f t h e m ou n ta in b l o c k as t h e more
s i g n i f i c a n t f a c t o r s in pedim entation,
t h e r e l a t i v e e f f i c a c y o f "backwear­
i n g " and "d o wn w ear in g" b e i n g d e p e n d e n t upon t h e i n i t i a l fo rm and s t a g e o f
142
the cycle.
R i c h (1935) f e l t t h a t f a n - l i k e form s may b e m a i n t a i n e d by
r u n n i n g w a t e r (without h a v i n g b e e n c a r v e d by i t
and t h a t l a t e r a l p l a n a t i o n
by s t r e a m s i s n o t n e c e s s a r y f o r t h e p r o d u c t i o n o f r o c k - f a n s and p e d i m e n t s ,
a l t h o u g h i t m ig h t c o n t r i b u t e t o w a r d t h e i r f o r m a t i o n .
He f e l t t h a t r o c k -
f a n s and p e d i m e n t s a r e r e m n a n t s , l e f t b e h i n d a s an e s c a r p m e n t o r m o u n ta in
f r o n t r e t r e a t s , and p r o t e c t e d from w a s t a g e by a v e n e e r o f g r a v e l i n t r a n s i t
w hi c h must be moved a c r o s s them .
The e s s e n t i a l f a c t o r s r e q u i r e d f o r t h e
p r o d u c t i o n o f p e d i m e n t s a r e w a s t i n g ( w e a t h e r i n g and t r a n s p o r t a t i o n )
sheetwash,
and
in c o n ju n c tio n w ith th e b la n k e tin g a f f e c t of a l l u v i a l d e b r i s .
R ic h c o n s i d e r e d v a r i o u s c o m b i n a t i o n s o f l i t h o l o g i e s
and t h e p r o b a b l e
r e s u l t s o f these c o m b i n a t i o n s i n t h e f i n a l p r o d u c t o f w e a t h e r i n g .
G illuly
(1938) a p p a r e n t l y a g r e e d w i t h R i c h b e c a u s e he w r o t e t h a t t h e
c o a l e s c i n g o f p e d i m e n t s a t t h e i r h e a ds t o g i v e b r o a d s u r f a c e s does not
support th e theory of l a t e r a l p la n a tio n because " i t
stream s could m igrate w idely at th e d i v id e s " .
i s d i f f i c u l t t o s e e how
He f e l t t h a t t h e d e v e lo p m en t
o f p e d i m e n t s i s c o n d i t i o n e d by t h e l i t h o l o g y o f t h e t e r r a i n ,
t h e s o f t e r and
more e a s i l y d i s i n t e g r a t e d r o c k s f o r m i n g more e x t e n s i v e p e d i m e n t s t h a n do t h e
h a r d e r and more r e s i s t a n t r o c k s .
Bryan (1 93 3 ) r e a c h e s s i m i l a r c o n c l u s i o n s
as a r e s u l t o f h i s s t u d i e s i n New Mexico, b u t he added t h a t
la te ra l plana­
t i o n may b e t h e more e f f e c t i v e p r o c e s s i n t h e p r o d u c t i o n o f more e x t e n s i v e
a re a s of pedim ents, p a r t i c u l a r l y in e a r l y s ta g e s o f th e c y c le .
He o b s e r v e d
t h a t p e d i m e n t s hav e l o w e r s l o p e a n g l e s o p p o s i t e l a r g e r s t r e a m s t h a n
o p p o s i t e s m a l l e r o n e s and t h a t
areas,
they a r e s t i l l
s t e e p e r in t h e i n t e r s t r e a m
t h u s b e i n g g e n e r a l l y c o n c a v e upward r a t h e r t h a n f a n - s h a p e d .
r e g a r d e d t h e common l a c k o f m ea n d e rs i n t h e s t r e a m s a s sh owing t h a t
He
143
l a t e r a l p l a n a t i o n does not dom inate in fo rm in g t h e p e d im e n ts .
B l a c k w e l d e r ( 1 929 ) m a i n t a i n e d t h a t p e d i m e n t s a r e t h e t y p e o f p l a i n
n o r m a l l y d e v e l o p e d d u r i n g q u i e s c e n t p e r i o d s i n a r i d r e g i o n s and t h a t
a l l u v i a l f a n s c a n n o t be made u n d e r s t a t i c c o n d i t i o n s .
He a t t r i b u t e d t h e
f o r m a t i o n o f p e d i m e n t s t o l a t e r a l p l a n a t i o n b u t he f e l t t h a t a b r a s i o n was
not th e c h ie f process involved.
In h i s o p i n i o n , w e a t h e r i n g p r e p a r e d
l o o s e r u b b l e f o r t h e f l o o d s t o sweep away.
)
S h a r p e ( 1 940 ) f a v o r e d l a t e r a l p l a n a t i o n a l o n g l a r g e p e r m i n e n t s t r e a m s
and i n a r e a s o f s o f t r o c k s b u t h e f e l t t h a t w e a t h e r i n g ,
r i l l wash,
r a i n wash a r e most e f f e c t i v e i n a r e a s o f e p h e m e r a l s t r e a m s ,
and low m o u n t a i n m a s s e s .
and
hard ro ck s,
"
He c o n s i d e r e d t h a t a l l v a r i a t i o n s from p e d i m e n t s
c u t e n t i r e l y by l a t e r a l p l a n a t i o n t o t h o s e formed e n t i r e l y by o t h e r p r o ­
cesses are th e o r e tic a lly possible.
The l a s t m a j o r p h i l o s o p h y i s b a s e d a l m o s t e n t i r e l y on l a t e r a l p l a n a ­
t i o n by s t r e a m s .
G ilbert
(187 7 ) s t a t e d t h a t t h e downward w ea r o f s t r e a m s
c e a s e s when t h e l o a d e q u a l s t h e c a p a c i t y f o r t r a n s p o r t a t i o n .
L ateral
corrosion
and c a r v e s
t h e n becomes r e l a t i v e l y and a c t u a l l y o f i m p o r t a n c e ,
an even s u r f a c e c o v e r e d by a t h i n d e p o s i t of. a l l u v i u m .
By c u t t i n g l a t e r ­
a l l y i n t o e a c h o t h e r ' s v a l l e y s and consuming a l l r e m n a n t s o f t h e i n t e r ­
vening d iv id e s ,
streams c o o p e ra te to c a rv e a s in g l e p l a i n o f broad e x te n t .
J o h n s o n (193 2) b u i l t h i s t h e o r i e s on t h i s p h i l o s o p h y w i t h c e r t a i n m o d i f i ­
c a t i o n s and i m p r o v e m e n t s .
l a t e r a l c u tt in g but t h a t
He f e l t t h a t v e r t i c a l c u t t i n g mu st accompany
t h e r a t i o o f t h e two was n o t c o n s t a n t .
t h e s t r e a m s f l o w f u r t h e r away from t h e m o u n t a i n s ,
more and more i m p o r t a n t .
T h u s , as
l a t e r a l c u t t i n g becomes
At g r e a t d i s t a n c e s from t h e m o u n t a i n s , t h e
144
s t r e a m s w i l l a c t u a l l y a g r a d e a few f e e t w h i l e m i g r a t i n g t h o u s a n d s o f f e e t
laterally .
F a u l ti n g , warping,
c l i m a t i c change o r simply d e c re a s e o f load
due t o c h a n g e s e f f e c t e d by e r o s i o n o f t h e c e n t r a l m ass, may c a u s e s t r e a m s
to e n tre n ch them selves in p lan e s o f l a t e r a l c o r r a s io n .
New p l a n e s a t
s u c c e s s i v e l y l o w e r l e v e l s u s u a l l y w i t h d i f f e r e n t a n g l e s o f s l o p e may be
formed.
J o h n s o n p o i n t e d o u t t h a t r e m n a n t s o f such s u c c e s s i v e p l a n e s a r e
common f e a t u r e s i n a r i d r e g i o n s ,
and b e a u t i f u l exa mpl es a r e p r e s e n t a l o n g
t h e f l a n k s o f t h e A t l a s M o u n ta i n s o f A l g e r i a ,
So ut h A f r i c a ,
i n New Z e a l a n d ,
among t h e f o l d e d m o u n t a i n s o f
and i n t h e s o u t h w e s t e r n U n i t e d S t a t e s .
H ig h -
l e v e l b e n c h e s on m o u n t a i n s w e r e c o n s i d e r e d by J o h n s o n t o b e i n n e r m a r g i n s
o f o nc e ' f a r - s p r e a d i n g p l a n e s o f l a t e r a l c o r r o s i o n .
Howard (194 2) a g r e e d w i t h J o h n s o n i n many p a r t i c u l a r s .
He em p ha si ze d
t h e f a c t t h a t t h o s e who f a v o r t h e l a t e r a l p l a n a t i o n h y p o t h e s i s o f p e d im e n t
f o rm a tio n a t t r i b u t e t h e r e c e s s i o n o f t h e mountain f r o n t to p l a n a t i o n not
o n l y by l a r g e m o u n ta in s t r e a m s b u t t o s t r e a m s o f a l l
p l a n a t i o n may be a c c o m p l i s h e d by s t r e a m s o f a l l
as w e l l a s t r i b u t a r i e s ,
sheetfloods.
sizes,
sizes.
Lateral
by d i s t r i b u t a r i e s
by i n d i v i d u a l c h a n n e l s o f a b r a i d e d s t r e a m ,
and by
Howard i n s i s t e d t h a t t h e w a t e r s c a u s i n g t h e r e c e s s i o n o f
s l o p e s b y " w e a t h e r i n g - r e m o v a l a s w e l l as t h o s e c a u s i n g l a t e r a l p l a n a t i o n ,
are graded.
The a n g u l a r j u n c t i o n m e n t i o n e d e a r l i e r was a t t r i b u t e d s o l e l y t o
la te ra l planation.
Howard f e l t t h a t i f a s t r e a m i s c o n f i n e d t o
a c h a n n e l on o ne s i d e o f a f a n , t h e o p p o s i t e s i d e may b e c o v e r e d by d e b r i s
th a t prevents recessio n of the foot of th e slope.
angle i s
lost,
b u t when t h e s t r e a m r e t u r n s ,
accumulated d e b r is but c u t
Tem porarily the sharp
i t may n o t o n l y remove t h e
l a t e r a l l y i n t o t h e m o u n ta in s l o p e and s h a r p e n
145
th e angle a g a in .
-
Howard sums up h i s t h i n k i n g by s a y i n g t h a t p e d i m e n t s a r e
d o m i n e n t l y t h e work o f l a t e r a l c o r r a s i o n .
P e d i m e n ts a r e fo rm ed by r e c e s s i o n
o f t h e b a s e o f a m o u n ta in s l o p e w hi ch may be c o n s i d e r e d t o be t h e head o f
th e pedim ent.
A l t h o u g h w e a t h e r i n g r em ov a l seems t o be r e s p o n s i b l e f o r
r e c e s s i o n o f t h e s lo p e above t h e b ase,
l a t e r a l c u t t i n g seems t o be r e s p o n ­
s i b l e fo r p r a c t i c a l l y every inch o f r e c e s s io n o f th e fo o t of th e slo p e.
Hence,
the process p rim a rily resp o n sib le for th e recession of the g re a te r
p a r t o f t h e m o u n t a i n f r o n t i s n o t t h e same p r o c e s s t h a t i s p r i m a r i l y
r e s p o n s i b l e f o r pediment fo rm a tio n .
A ll o f t h e a b o v e i d e a s as w e l l as o t h e r i d e a s t h a t ha v e n o t been
m entioned,
h a v e some m e r i t b u t no one o f them i s an i d e a l s o l u t i o n o f t h e
p r o b le m o f p e d i m e n t f o r m a t i o n .
sp e cific areas;
Some o f t h e t h e o r i e s a r e a p p l i c a b l e i n
o th e r s in e n t i r e l y d i f f e r e n t a r e a s .
I cannot evalu ate
t h o s e t h e o r i e s w h ic h a p p l y t o s i t u a t i o n s f o r e i g n t o m y . e x p e r i e n c e .
In t h e a r e a s o u t h w e s t o f t h e C r a z y M o u n ta i n s ,
J o h n s o n and Howard ha ve much t o recommend them .
the philosophies of
My f i e l d o b s e r v a t i o n s
tended to s u b s t a n t i a t e Jo hnson's l a t e r a l p la n a tio n theory;
indeed i t is
d i f f i c u l t t o c o n c e i v e o f any o t h e r p r o c e s s h a v i n g formed t h e s u r f a c e s n e a r
t h e Crazy Mountains.
G ilb e rt's c la ssic a l
s t a t e m e n t s ( p a g e 75) on l a t e r a l
c o r r a s i o n a r e v e r y c l e a r and q u i t e p e r t i n e n t t o t h i s a r e a .
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^
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1
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